1 BERK UNIVERSITY OF CALIFORNIA EARTH SCIENCES LIBRARY GIFT OF Estate of Trip "R!- T.e < . ' ' % THE GEOLOGICAL STORY BRIEFLY TOLD. Introtwrtion to FOR THE GENERAL READER AND FOR BEGINNERS IN THE SCIENCE. BY JAMES D. DANA, LL.D., // AUTHOR OF "A MANUAL OF GEOLOGY," " TEXT- BOOK OF GEOLOGY," "CORALS AND CORAL ISLANDS," WORKS ON MINERALOGY, ETC. WITH NUMEROUS ILLUSTRATIONS. NEW YORK AND CHICAGO : IVISON, BLAKEMAN, TAYLOR, AND COMPANY. 1875. 50 MAKING OE ROCKS. is distributed along the borders, making sand-flats, mud-flats, and ultimately good dry land, to widen the serviceable area of the continent. The banks and bottom of a river are generally made of coarser or finer material, according to its rate of flow in the different parts. Where it is very slow the bottom and banks are sure to be of mud, for the very slow movement of the waters gives a chance for the finest detritus to settle; but if rapid it will consist of pebbles, if the region contains them. The bank struck by the current is, in general, more pebbly than the opposite. The action of the waters of large lakes in rock-making is to a great degree the same as that of the ocean. 5. The Work of the Ocean. The mechanical work of the ocean has been carried forward chiefly through (1) its tidal movements ; (2) its waves ; and (3) its currents. 1. Tides. With each incoming tide the waters flow up the coast and into all bays and mouths of rivers, rising several feet and sometimes yards above low-tide level; and then, with the ebb, the same waters flow back and leave once more the mud-flats and sand-banks of the bays and coasts exposed to view. This retreat of the tide allows the rivers to discharge freely and carry out their detritus to sea ; but soon again the inflow stops the movement outward and reverses it, and dur- WORK OE THE OCEAN. 51 ing the time of slackened flow the waters drop their detritus, part about the mouth of the stream, part along the adjoin- ing coast, and part in the shallow waters of the sea outside. 2. Waves. The sea in its quiet state is rarely without some swell, which causes at short intervals a gentle movement on the beach and some rustling of the waters along rocky shores. Generally there are waves and breakers; and when a heavy storm is in progress the waves rise to a great height and plunge violently upon the beach and against all exposed cliffs, wave following wave in quick succession through days or it may be weeks together. With each storm the waves renew their violent strokes, and in many seas the action is incessant. * The plunge on the beach grinds the stones against one an- other, rounding them and finally reducing them to sand, and the sand to finer sand. The waters after the plunge retreat down the beach underneath the new incoming wave; and this " undertow " carries off the finer sand made by the grinding to drop it in the deeper waters off the coast, leaving the coarser to constitute the beach. Thus wave-action grinds to powder and removes the feldspar and other softer minerals of the sand, and leaves behind the harder quartz grains; and consequently, wherever there are beaches of sand, there are offshore deposits of mud made out of the fine material carried seaward by the undertow. In no age of the world have sand-beds been formed without the making of mud-beds somewhere in their vicinity. 52 MAKING OE ROCKS. The cliffs, or exposed ledges of rock, are worn away under the incessant battering, and afford new stones and sand for the beach, and the shallow waters adjoining. Most rocky shores, especially those of stormy seas, show, by their rugged cliffs, needles, arches, and rocky islets the effects of the storm- driven waves. It is to be remembered that the ocean, as stated on page 42, often finds the work of destruction facilitated by the weakening or decomposition the rocks have undergone through the quiet action of air and moisture, and also through other means explained beyond (page 63). The waves, as they move toward the shores over the shelv- ing bottom, bear the sediment in the waters shoreward, and throw more or less of it on the beach. And thus the beach grows in extent. The sediment is, in general, either what it gets from the battered rocks of the coast, or what the rivers pour into the sea. At the present time the Atlantic receives an immense amount of detritus through the many large streams of Eastern North America; and as a consequence the shores aa-e extensive sand-flats from New York southward, with shal- low sounds inside ; and the latter are the spaces not yet filled to the water-level with the deposits of detritus. The coast has been growing seaward for ages through the same means, with but little aid from the wear of sea-shore cliffs. But in the earlier geological ages this was not so; for the continent was to a large extent more or less submerged, and the waves WORK OP THE OCEAN. 53 made a free sweep over its surface, battering the rocks in many places, and thus making its own sediment; for there were only small streams on the small lands to give any help. In the warmer seas of the world mollusks are very abundant. The heavier storm-waves tear them from the muddy bottom where they were alive, and throw them on the beach. There they are exposed to the incessant grinding which stones and ordinary sands experience elsewhere, and thus are reduced to sand. Every storm adds to the shells of the beach as well as to the shell-sand. Thus sand-deposits form that are made out of shells alone; and they keep growing and may become of great extent. The finer shell-sand is swept out into the shallow waters, and there produces a finer deposit. The hard- ening of such deposits makes limestone ; and the shells that happen to escape the grinding are its fossils. In this way limestones have been made in all geological ages. Shell rocks are now forming at St. Augustine, Florida, and the limestone there made is used as a building-stone. In other parts of tropical seas there are corals growing profusely within reach of the waves, or within 100 feet of the surface. Many are broken or torn up by the waves and carried to the beach, and there are ground up and spread out in beach deposits and off-shore deposits. These beds of coral sand or mud harden, and then become the coral reef rock, - a true limestone, similar to many of ancient time. South of Florida, and in other parts of the West Indies, in various 54 MAKING OF ROCKS. parts of the tropical Pacific, and also in the East Indies and Red Sea, these coral limestones are now in progress. 3. Currents, The ocean has its system of circulation, or of great currents. The Gulf Stream is part of it; its waters, flowing westwardly in the tropical Atlantic, bend northward as they pass the West India seas, and then pass northeast- ward, parallel with the North American coast as far as New- foundland, gradually curving eastward. Thence a part continues either side of Iceland to the Arctic seas, from which there is a return, as a cold Labrador current, along the coast of Lab- rador and farther south. This great current moves but 5 miles an hour when swiftest, and this only in part of the straits of Florida. Its average rate, parallel with North Amer- ica, is 2i miles an hour; and it is hardly felt at all anywhere along the sides of the continent, not even in the Florida straits. It hence gets no detritus from the wear of coasts, and is too feeble to carry anything but the very finest silt. The ocean's bottom shows that it receives almost nothing either in this way or from the currents of great rivers. When, however, the continents were submerged a few hundred feet or less in ancient time, the currents swept over the surface, and must have done much work in wearing rocks and trans- porting detritus. Both waves and gentle currents raise ripples over the sands; and such ripple-marks, made by the ocean in ancient times, are often preserved in the rocks (Fig. 49). They show that WORK OF THE OCEAN. 55 the sands of which the rocks were there formed were within reach of waves or gentle currents. The mud of a mud-flat or of a dried-up puddle along a roadside is often found cracked as a consequence of drying; and such mud-cracks are frequently preserved in sedimentary rocks (Fig. 50). They are of great interest to the geologist; for they show that the layer in which they occur was not of Figs. 49, 50. 49 Ripple-marks. Mud-cracks. deep- water origin; but beyond question was exposed, for a while at least, above the water's surface to the drying air or sun, as mud is now often exposed along a roadside, or over the mud-flats of an estuary. Such cracks become filled with the next deposit of detritus, and this filling has often been afterward so consolidated as to be harder than the rock out- side; and hence on a worn surface the fillings of the cracks 56 MAKING OF ROCKS. Fig. 51. Rain-drop impressions. generally make a network of little ridgelets, as in the pre- ceding figure. Again, mud-flats sometimes have the surface covered with rain-drop impressions after a short shower in which the drops were large; and many shales (rocks made of mud or clay) retain these markings (Fig. 51) ; others have impressions of the footprints of animals, even those of insects. Such delicate impressions are preserved, because soon after they are made they be- come covered with a layer of fine detritus; and after that nothing can erase them short of the removal of the deposit itself. The rocks that have been made by fresh waters and the oceans are of vast extent. They are the sandstones, conglom- erates, and shales of the world; and they include the limestones also. The ocean has done far the larger part of the rock-mak- ing. In the earlier geological ages it worked almost alone; for the lands were very small, and only large lands can have large rivers and river deposits. Afterward, in the coal-era, there was at least one large delta or estuary on the borders of the American continent, that of the St. Lawrence; and ever since rivers have given important aid. During the last of the ages, after the continents had reached nearly their present extent, WORK OF ICE. 57 and the mountains their modern height and numbers, rivers have done the larger part of the distribution of rock-material. Sedimentary rocks show that they were formed through the action of water, often in the rounded or water-worn pebbles they contain, or the water-worn sand, or from a resemblance in constitution to a consolidated bed of mud or clay; in their relics of aquatic life, and the indications of wave-action or cur- rent-action above pointed out; and in their division into layers, such as exist in known sediments or deposits from waters. 6. The Work of Ice. 1. Expansion on freezing. When water freezes it expands. If it freeze in a pitcher, the expansion is pretty sure to break the pitcher. If it freeze in the crevice of a rock, it opens the crevice; and by repeating the process winter after winter in the colder countries of the globe, it pries off and breaks apart rocks, and makes often a slope of broken blocks, or talus, at the foot of a bluff. By opening cracks in this w r ay it gives air and moisture new chances to do their quiet work of destruction. 2. Transportation by the ice of rivers or lakes. When water freezes over a river it often envelops stones along the shore ; and then, whenever there is a breaking up, the ice with its load of stones is often floated off down stream; or if the water of a stream or lake rises in consequence of a flood, the stones may be carried farther up the shore and dropped there. In cold countries ice often forms thickly about the stones 3* 58 MAKING OF ROCKS. in the bottom of a stream; and as it is lighter than water it may become thick enough to serve as a float to lift the stone from the bottom, so that both ice and stone journey together with the current. These are commonplace ways in which ice does geological work. Its greater labors are performed when it is in the condition of a glacier. 3. Glaciers. Glaciers are broad and deep streams of ice in the great valleys of snowy mountains like the Alps. The snows that fall about the summits above the level of perpetual snow accumulate over the high region until the depth is one or more hundred feet. At bottom it is packed by the press- ure and becomes ice. Its weight causes the ice to descend the slopes of the mountains and along the valleys, which it fills from side to side. The width of the ice of the valley may be several miles; its depth in the Alpine valleys is gen- erally from 200 to 500 feet. ' The glaciers descend far below the line of freezing to where the fields are green and gardens flourish; and this takes place because there is so thick a mass of ice. In the Alps the glaciers stretch down the valleys 4,500 to 5,300 feet below the snow-line. At Grindelwald two glaciers terminate within a short distance of the village. The rate of movement in the Alps in summer is mostly between 10 and 20 inches a day, and half this in winter; 12 inches a day corresponds to a mile in about 14i years. WORK OF ICE. 59 Fig. 52 (from a sketch in one of Agassiz's works on glaciers) represents one of these great ice-streams or glaciers descending a valley in the Monta E/osa region of the Alps. A valley often narrows and widens at intervals, and changes its slope at times Fig. 52. Glacier of Zermatt, or the Corner Glacier. from a precipitous to a horizontal surface. The ice has to ac- commodate itself to all these variations. On turning an angle it is broken, or has great numbers of deep continent was receiving marine deposits. The areas in North America, east of the Rocky Mountain region, and over which Silurian rocks are exposed to view, are those which are lined horizontally in the map on page 105. The Silurian regions in England are distinguished in the same way on the accompanying map (Fig 91) ; they are confined to Western England and Wales. 1. Lower Silurian. 1. Bocks. The rocks of the Lower Silurian era are mainly sandstones]\ x shales, conglomerates, and limestones. The same is true for all succeeding eras in geological his- tory; for sand-beds (the source of sandstones), mud-beds (the source of shales and argillaceous sandstones), and limestones have been always in progress from this time onward in some part of each continental region. Moreover, sand-beds have never been forming in any region without the making of mud- beds in the waters not far distant, just as now happens along sea-shore regions ; for the grinding which produces the former produces also the latter. Nevertheless, the continental areas 116 PALEOZOIC TIME. over which sand-beds, mud-beds, and limestones were accu- mulating have varied greatly through the successive periods, owing to variations in level and other causes; and at times the larger part of the continental sea has been given up to limestone-making. The following is the succession of Lower Silurian rocks in North America. 1. In the early part of the era, called the Primordial (meaning the first in order] , sand-beds now called the Pots- dam sandstone, from a locality in Northern New York were spread out over wide areas in North America, and especially about the shores of the Archaean dry land ; but shales and lime- stones were forming in some places more or less remote from these shores. These earliest Silurian sandstones and shales have the layers sometimes marked with ripples, or with mud-cracks, or with the tracks of the animals of the era ; and they thus show that they were not made in deep water, but, instead, that they were either the sea-beaches or the off-shore sand-flats or mud-deposits of the era ; and that part of the time they were above the water's level, exposed to the drying air or sun, for only thus can mud- cracks be made. 2. As the era advanced, limestone strata (magnesian lime- stones, mainly) of great extent were formed over the region of the Mississippi Yalley, or the Interior region of the continent, while sandstones and shales with but little limestone were ac- LOWER SILURIAN. 117 cumulating in the area then a shallow sea now occupied by the Appalachian Mountains. 3. Next a limestone the Trenton limestone was in pro- gress over both the Appalachian region from the Green Moun- tains to Alabama and the Interior region, and also far west and north, the most extensive limestone formation in the world's history. The limestone was named from Trenton Falls, on West Canada Creek, near Utica, New York, where the gorge is cut through it. It includes the Galena or lead-bearing limestone of Illinois and Wisconsin. 4. Finally, limestone-making was again confined almost wholly to the Interior region, and the Appalachian area, in- cluding New York and the Green Mountains on the north, was receiving fragmental deposits for sandstones, shales, and conglomerates. In Great Britain there are, first, slates and sandstones of great thickness in the Longmynd and Wales, overlaid by the " Lingula flags " (the equivalent of the Potsdam sandstone) ; above these, other slates and flags (laminated sandstones), with some layers of limestone, including the Llandeilo flags, the Bala beds, and the Lower Llandovery in South Wales, all making one con- formable series. 2. Life. The seas abounded in life, but no trace of anything terres- trial has yet been found. The plants found are aft sea-weeds. One of the specimens 118 PALEOZOIC TIME. is represented in Pig. 92. Some thin deposits of coal occur in one of the formations, which are supposed to have come from buried sea-weeds, or else from animal material. The animals are all Invertebrates ; in other words, no trace of a Vertebrate, not even of the lowest of Fishes, has yet been discovered among the animal relics. But all the four sub- kingdoms of Invertebrates are represented, the Protozoan, the Eadiate, the Molluscan, and the Articulate. Figs. 92, 93. Sea-weed. Sponge. Fig. 92, Buthotrephis gracilis ; 93, Archsepcyathus Atlanticus. Protozoans, Among Protozoans there were Rhizopods and Sponges. One of the Sponges is represented half the natural size in Pig. 93 a, and a transverse section of it, natural size, in Pig. 93 b. The irregular cellular structure, with the absence of radiating plates, is evidence that it is not a coral. Radiates. The Radiates include Corals, Crinoids, and Star- fishes. Pig. 94 is a side-view of one of the conical corals of the Trenton limestone; the top is a cup, radiated with plates, somewhat like Pig. 15, page 29. When living, the flower-like LOWER SILURIAN. 119 animal had no doubt its beautiful colors, like those of modern time, and its aspect may be quite well represented by Fig. 16, page 30. Figs. 94, 95. Polyp-Corals. Fig. 94, Petraia corniculum ; 95, Columnaria alveolata ; 95 a, top view of same. Another coral, honeycomb-like in its columnar structure, is represented in Fig. 95. The cells are radiated, as shown in Fig. 95 ; but in a vertical section (as seen in such a section of one of the cells in Fig. 95 a) the cells are crossed by horizon- tal partitions. The coral has been found in masses several feet in diameter. Figs. 96-99 represent some of the Crinoids and Star-fishes. Fig. 97 shows one of the Crinoids of the Trenton limestone, though not quite a perfect one, as the arms are broken off at the tips, and the stem below (by which it was attached to the rock of- the sea-bottom, and which may have been three or four inches long) is mostly wanting. The name Crinoid means lily- \ like; but the petals or rays of the flower-like animal consist of small pieces of limestone (the secretion of the animal) fitting well together. Fig. 96 shows the form of another kind of Crinoid, one of very irregular shape; its stem when living 120 PALEOZOIC TIME. was run down into the mud of the sea-bottom, instead of being attached to a rock. Figs. 98, 99 are two of the Star-fishes of the ancient seas, related to the modern Ophiurans. Figs. 96-99. Fig. 100. Asterioids. - Crinoids. Fig. 96, Pleurocystis filitextus ; 97, Lecanocrinus elegans Crinoids : Fig. 98, Palaeaster matutina ; 99, Taeniaster spinosa. Mollusks. The Mollusks were of various kinds, all the principal grand divisions of the class having been represented by species. Par the most abundant were what are called Brachi- opods, a group that has comparatively few kinds in modern seas. One of the earliest Brachiopods from the Potsdam sandstone had a shell not larger than a finger-nail; a large specimen of it is rep- resented in Fig. 100. It is called a Lingnla (or Lingulella) , from the Latin lingua, a tongue, in allusion to the tongue-like shape of some species. A related species is found in the Lingula flags of Great Britain. "When living LOWER SILURIAN. 121 it was fixed to the sea-bottom by a fleshy stem proceeding downward from the pointed end or beak of the shell, and passing into the mud or sand; and as the shells are often in great numbers together, they must have grown thickly over the sandy or muddy surface. Other common Brachiopods from the Trenton limestone are represented in Figs. 101 to 104. Figs. 101-104. 102. Fig. 105. Brachiopods. Fig. 101, Leptaena sericea ; 102, Orthis occidentalis ; 103, O. lynx ; 104, O. testudinaria. The shells have two valves like those of a clam or oyster; but they are unlike common Bivalves in their symmetrical form; a line let fall from the beak divides them into equal halves, whereas in a Clam, as shown in Fig. 105, such a line divides the shell very unequally. Moreover, the mouth in a Brachiopod is at the middle of the shell, whereas in common Bivalves it is toward one end (near a, in Fig. 105) ; and further, one valve is the upper and the other the lower, while in a Clam, and related kinds, one is the right and the other the left. Thus the 6 122 PALEOZOIC TIME. animal in this ancient group called Brachiopods has a posi- tion in its shell just transverse to that of a Clam. The ani- mal is also peculiar in having two spiral fringed arms, and to FI ice ^i s the name, from the Greek for arm-foot, alludes. Fig. 106 shows these arms in a modern species ; one of the pair is rolled up spirally in its ordinary position, while the. other is thrown out. The animal has no gills or branchiae. The Trenton limestone was made largely of the shells of Brachio- Khynchonella psittacea. ^ Crmoids and Corals havmg contr ibuted little toward it. The Clam and Oyster and other ordinary Bivalves have a thin fold of the skin lying like a mantle over the body against the shell ; then, inside of the mantle and either side of the body, thin leaf-like gills or branchiae ; and then the body with no arm-like appendages. In allusion to the thin lamellar branchiae, they are called LamellibrancJis. There were some Lamellibranchs in the Lower Silurian, but they were few compared with the Brachiopods. Fig. 107 represents one of them, related to the Mussel of modern sea-shores. There were also some spiral shells, two of them of the forms shown in Figs. 108, 109. They belong to the tribe of Gasteropods, so called because the animal crawls on its ventral surface. The ordinary spiral marine shells, and also the common snail, are of this tribe. The snail may be often LOWER SILURIAN. 123 Figs. 107 - 109. seen crawling thus with its shell over its back; and the marine species when living, if put into a jar of salt water, will soon be found in motion over the glass. There were also many species of the highest di- vision of Mollusks, those related to the Nau- tilus, and called Cephal- j because the animal Fig. 110. Mollusks. haS the head furnished Fig. I07> Avicula Trentonensis ; 108, Murchisonia bicincta ; 109, Pleurotomana lenticularis. with stout arms for cling- ing; from the Greek for head and feet. A modern Nautilus, with the animal in its shell, is represented in Fig. 110. The shell has transverse partitions, or is chambered, and in this differs from the shell of the Snail and all Gasteropods. The animal oc- cupies the large outer chamber, and is peculiar in having large eyes like a fish, and a series of stout arms around the mouth provided with suckers for cling- ing. A different kind of Cephalopod, from modern seas, is represented in Pig. Ill, a kind having no external shell, but instead a thin internal bone (Pig. Ill jo), but with Modern Cephalopod. Nautilus (X #). 124 PALEOZOIC TIME. large eyes and a series of arms around the mouth, as in the Nautilus. In the Lower Silurian era there were spe- cies of Nautilus, but quite different ones from those of later Fig. 111. Modern Cepbalopod. The Caiamary or Squid, Loligo vulgaris (length of body, 6 to 12 inches) ; *', the duct by which the ink is thrown out; f, the "pen." time. But the earliest Silurian species of Cephalopods and the largest had straight shells, like that of a Nautilus straight- ened out, whence the name Orthoceras, meaning a straight horn. One of them, from the Trenton limestone, is represented in Pig. 112 ; it has partitions like the shell of the Nautilus. Fig. 112. Cephalopod. Orthoceras junceum. In both the Nautilus and the Orthoceras a tube (called the siphuncle, meaning little siphon) passes from the outer cham- ber through the partitions and all the chambers ; and the hole in one of the partitions is shown in Pig. 112 a. Some LOWER SILURIAN. 125 of the shells of species of Orthoceras from the Trenton lime- stone are as large round as a flour-barrel, and must have been from twelve to fifteen feet long. Another kind of Mollusk, of quite minute size, makes cor- als. The animals look like polyps externally, as shown in Fig. 113, which represents them enlarged, projecting out of their cells. Fig. 114 is a view of one of the deli- cate Lower Silurian cor- als, and the dots show the positions of the little cells of the animal. The Figs. 113, 114. Bryozoans. - p .^ ii3 Eschara> snowing aniin al s extended out of their cells ( X 8) ; 113 a, one of the animals removed from its cell more en- - larged; 114, Ptilodictya fenestrata, a Lower Silurian species, natural size ; 114 a, portion of surface of same enlarged. are CalleCl meaning ma Is, the name alluding to the corals, which are sometimes moss-like in delicacy and form. Although so small, these corals are a prominent con- stituent of some of the Silurian limestones. Articulates. The Lower Silurian Articulates that have been made out are either Worms or Crustaceans ; no Insects or Spi- ders having been present, since these are terrestrial species. The most remarkable of the Crustaceans, and the highest spe- cies of the world at the commencement of Lower Silurian time, and later in this era second only to the Orthocerata, were the Trilobites, so named because the body has three lobes or divisions longitudinally, as shown in Figs. 115 to 117. One 126 PALEOZOIC TIME. of the very earliest species is represented in Pig. 115; it was a gigantic species, the figure being only one third the natural length. It has some resemblance to a lobster, and yet is very different. The position of the large eyes is apparent on the Figs. 115-118. Trilobitcs. Fig. 115, Paradoxides Harlani (X }4); 116, Asaphus gigas (X #) ; 117, Calymene Blumenbachii j 118. same rolled up, as it is often found. head shield. Two other species, from the Trenton, are repre- sented in Pigs. 116, 117. The latter is shown folded up in Pig. 118, a common condition of the specimens. The forms of three modern species of Crustaceans having some resem- LOWER SILURIAN. 127 blance to the ancient Trilobites are shown in Pigs. 119 to 122. Figs. 121, 122 are female and male of the same species. But the Trilobites differed from Figs. 119-122. all these in having had no true legs. They are supposed to have had only thin fleshy plates, for swimming. The earliest life of the Modern Crustaceans. Lower Silurian was made Fig . 119(aspeciesof Serolis(x ^ ); I2o spedesof Porcel . , . />/-< i lio ' 181 I22 female and male o{ Sapphirina iris. up largely or urinoiqs, Brachiopods, Worms, and Trilobites. It was almost all sta- tionary life; that is, the most of the species were attached to the sea-bottom by stems. Such were all the Crinoids and Brachiopods. Trilobites swam free; but, having only swim- ming legs, they probably often attached themselves to the rocks, like the shells called Limpets. Afterward there were Mussel- like shells and corals, which were also attached species, Mus- sels living attached to rocks by a byssus or horny threads. Besides these there were the locomotive species, Gasteropods and Orthocerata; the latter may have given much activity to the seas, for Cephalopods are not snail-like in pace, like all Gasteropods, but fleet movers, like fishes. Yet these ancient species, with their long unwieldy shells, must have been slow \ compared with the Cephalopods of later time. The life of the Lower Silurian changed much in species dur- ing its progress. The era has been divided into three periods : 128 PALEOZOIC TIME. no animals of the earlier part of the first of these periods / the Primordial existed in the second, and none of the earlier part of the second existed in the third. Moreover, ; species were disappearing and others appearing through each of the successive periods. 3. Mountain-making. The close of the Lower Silurian was a time of upturning and mountain-making in North America, Great Britain, and I Europe. The Green Mountains, from Canada to southern Con- necticut, and perhaps other heights to the southwest, were then made. The rocks which include a great limestone for- mation (the upper part of which is referred to the Trenton) and also various fragmental rocks overlying the limestone were folded and crystallized by the heat produced by the dis- turbance added to that from the earth's depths, and were thus changed at the time to metamorphic rocks : the fossiliferous limestone, to white and clouded crystalline or architectural mar- ble, of which Canaan in Connecticut, Lee in Massachusetts, and Eutland in Vermont afford noted examples; the quartzose sand-beds, to quartzyte; the mud-beds, to gneiss, mica schist, and other crystalline rocks. In Great Britain the Lower Silurian formations, which are throughout conformable, are upturned so as to lie unconform- ably beneath the beds of the next era, the Upper Silurian. The elevation of the Westmoreland Hills, of the mountains in UPPER SILURIAN. 129 North Wales, and of the range of Southern Scotland from St. AbVs Head, on the east coast, to the Mull of Galloway, has been referred to this era. The maximum thickness of the Lower Silurian rocks of > Britain has been stated to be over 40,000 feet. In the Green - Mountain region it was probably not less than 20,000 feet; in Pennsylvania, about 11,000 feet; in Illinois, about 800; in Missouri, nearly 2,200 feet. 2. Upper Silurian Era. 1. Bocks, The rocks of the Upper Silurian also are sandstones, con- glomerates, shales, and limestones. 1. There was first in progress, during what has been called the Niagara period, the formation which includes the Niagara limestone, which, like the Trenton limestone, was one of the great limestone formations of ancient time. In Western New York and to the southwest along the Appalachian region still a part of the continental sea the earlier beds forming were a series of sandstone strata (the Medina sandstone), some- what pebbly below and argillaceous above; then other argil- laceous sandstones, and in them a bed of red iron ore, with a little limestone in the upper part; then the Niagara shale and limestone, the strata at Niagara Palls, where the upper 80 feet are limestone and the lower 80 feet shale. To the west of New York, the Niagara shale formation is of little extent, 6* i 1:30 PALEOZOIC TIME. while the limestone spreads very widely, reaching into Iowa and Tennessee. / The layers of the Medina sandstone often have ripple-marks, '; mud-cracks, wave-marks, and other evidences of mud-flat or 7 ^ sand-flat origin, showing that Central and Western New York, with the region to the southwest, was then an area of great sand-flats over an interior sea; but later this interior sea was more open and clearer; so that there was less sediment, and the life required for making limestones flourished. In Great Britain the Wenlock shale and limestone are of the age of the Niagara shale and limestone. They are in view between Aymestry and Ludlow, near Dudley, and else- where. The limestone, like the Niagara, is full of fossils. 2. Afterward the Salina formation, noted for its salt, was made. Its clayey rocks and salt show that Central New York, the borders of Canada to the west, and part of Michigan were then the site of a great salt basin, where sea-water evaporated, impregnating the mud of the shallow sea with salt, or making deposits of rock-salt. The brines of Salina and that vicinity I [ in New York are salt-water wells, obtained by boring down to this saliferous rock; and at Goderich in Canada there is a bed of rock-salt 14 to 40 feet thick. Other salt-bearing / rocks were made at the same time in Virginia. 3. Next followed another limestone formation of less extent than the Niagara, called the Lower Helderberg, from the Hel- derberg Mountains southwest of Albany, where it occurs. It UPPER SILURIAN. 131 extends southwestward along the Appalachians; also through parts of the Mississippi Valley where it rests directly on the Niagara limestone. It also occnrs at some points in the Con- necticut Yalley. A sandstone the Oriskany sandstone overlies it in Central New York and along the Appalachian region, and in some places to the west, from Ohio to Missouri. Following the "Wenlock group in Great Britain there is the Ludlow group, consisting of sandstones, shales, and the Aymestry limestone, corresponding in age with the later part of the American Upper Silurian. 2. Life. 1, Plants. As in the Lower Silurian, sea- weeds were abun- dant; but before the close of the era there were also terrestrial j plants. The species were not Mosses of the lower division of Cryptogams, or flowerless plants, and not Grasses, but species of the Ground-Pine tribe, or Lycopods, a section of the highest) Cryptogams. They are described beyond, in the account of the Devonian plants. It cannot be affirmed that there were no Lichens or Fungi over the Silurian rocky lands, or those of earlier time ; for such terrestrial species, if existing, would not have become fossilized, since the rocks are mainly of marine or marsh origin. But that there were no Mosses may be safely inferred from the absence of all fossil Mosses from the rocks) of the following Devonian and Carboniferous ages. 2, Animals. The animals included species of all the grand 132 PALEOZOIC TIME. divisions existing in the Lower Silurian, Protozoans, Radiates, Mollusks, and Articulates, with the same great preponderance of Brachiopods among Mollusks, and Trilobites among Articu- lates. In addition, before the close of the era, there were Eishes in the seas, the earliest of Vertebrates. No remains of terrestrial animal life have yet been found. A few figures of the Invertebrates are here given. Pigs. 123, 124 represent two of the corals of the Niagara period; Figs. 123-125. Polyp-Corals. Crinoid. Fig. 123, Zaphrentis bilateralis; 124, Halysites catenulata. Crinoid : Fig. 125, Stephanocrinus angulatus. Eig. 123 related to the coral of the Lower Silurian, figured on page 119; Eig. 124, a coral imbedded in limestone, which looks, in a section of the limestone, a little like a chain, or a string of links, and has hence been called Chain-coral. Eig. 125 shows the form of one of the Niagara Crinoids. Some of the more common Bracniopods of the Niagara group are represented in Eigs. 126-128. UPPER SILURIAN. 133 Figs. 126-128. 127 BracMopods. Fig. 126, Strophomena rhomboidalis ; 127, side-view of Spirifer Niagarensis ; 128, Orthis bilobus ; 128 a, enlarged view of same. The following are figures of two of the larger Trilobites. Both figures are reduced views, Eig. 129 being but one third the natural length, and Fig. 130 one fourth. Figs. 129, 130. Trilobites. Fig. 129. LichasBoltoni(X tf); 130, Homalonotusdelphinocephalus(X ja The fishes were related to the modern Sharks and Gars. Descriptions of the kinds are given under the Devonian, the specimens of Devonian rocks being more perfect and afford- ing better illustrations of the subject. 134 PALEOZOIC TIME. 3. Observations on the Silurian Age. 1. The distribution of the emerged lands of North America at the close of Archaean time led us to the conclusion (page 108) that the continent was then already denned in area, and its plan of future progress made manifest. The facts respect- ing the Silurian rocks sustain this view, and show how the work of completing the continent went on through the Silu- rian era. It has already been explained, by reference to the map of the Archaean dry land, on the same page, that rock- making, and therefore progress, was confined to the submerged part of the continent. The map shows the position of the coast-line along which the waves broke when the Silurian age began, making the sea-beach deposits and sand-flats that now form part of the Potsdam sandstone. The Appalachian region must have been one of the areas of great sand-flats or reefs, for its eastern side was the course of a range of Archaean mountains ; and the Rocky Mountain region, for the same reason, was probably another of the shallower portions of the continent. The Lower Silurian continental sea had its great- est depth over the intermediate Interior region, of which the present Gulf of Mexico was then the southern part. These in- ferences are sustained by the whole course of the history. 2. With the progress of the Silurian the dry land of the north received a gradual extension southward, southeastward, and southwestward. This was the direction of growth. Shore- SILURIAN AGE. 135 lines of the successive periods were more and more remote from the old Archaean sea-shore, for the limits of the suc- cessive formations are farther and farther south; so that, at the close of the age, the coast-line in the region of the mod- ern State of New York probably lay a little to the south of the present Mohawk valley, and, extending westward from Niagara over Western Canada, it bent northward around Lake Huron ; thence it turned southward so as to cross Northern Illinois before taking its course to the far north parallel with the west side of the Archaean nucleus. These conclusions are deduced from the limits of the Silurian formations, shown on the map on page 105. 3. At the close of the Lower Silurian the Green Mountains were made by an upturning and crystallization of the rocks. A new area of dry land was thus formed between the seas of New York and New England, and the valley of Lake Cham- plain was a consequence of the uplifting. There was also an upward bending of the earth's crust, but without upturning, over an area from Lake Erie across the Cincinnati region to Tennessee, making another spot of dry land. The Green" Mountains were raised parallel to the neighboring Archaean Adirondacks ; the Cincinnati uplift was parallel nearly to the Archaean Blue Eidge. Thus progress was strictly after the plan laid down in Archaean time. Southern and Western New York, and the region of the Alleghany Mountains, remained within the limits of the con- tinental sea through the Silurian age. 136 PALEOZOIC TIME. 4. The rocks of the Interior region of the continent (now the great Mississippi valley) were mainly limestones from the beginning of the Silurian to its close; while those of the Appalachian region were mainly sandstones, conglomerates, and s/iales. The Trenton limestone spread over both; but, in general, there were fragmental deposits forming over the Ap- palachian region at the same time that there were limestone deposits in progress to the west of it. The Trenton lime- stone is an exception; but before the Trenton period closed the Interior region was alone in limestone-making, the Appa- lachian having become again, as the rocks show, an area of mud-flats and sand-flats. These facts prove that the Appalachian region was a great reef region through the era, and that over the interior of the continent there was at the same time a clear and wide sea, one seldom swept by sediment-bearing currents. The limestones were made of shells, crinoids, and corals mostly ground up; and their freedom in general from much impurity shows that the marine life had there the pure waters in which it best thrives. Several of the sandstones and shales contain ripple-marks, mud-cracks, or foot-prints, proving that they were made, not in a deep sea, but in shallow waters, and that the deposits were sometimes exposed above the water's surface. C5. Over 10,000 species of fossils were described from Lower and Upper Silurian rocks up to the year 1872. The species DEVONIAN AGE. 137 continued to change through the Upper Silurian era as well as the Lower Silurian; that is, the species of the early part had nearly all disappeared and new species had become sub- stituted before the later part of the era began; and each of the successive subdivisions in the rocks indicates some old fea- ture lost during its progress or in the transition, and some new feature gained. 2. Devonian Age, or Age of Fishes. The term Devonian was first applied to the rocks of the age in Great Britain by Sedgwick and Murchison, and al- ludes to the region of South Devon, where the rocks occur and abound in fossils. Through the age the land had its plants and insects, and the seas their numerous fishes, besides species of all the lower orders of life. The regions of Devonian rocks are those ver- tically lined on the North American map, page 105, and the map of England, page 114. 1. Rocks. The Lower Devonian rocks of North America overlie con- formably the Upper Silurian, making a continuous series with them. The age commenced with the era of the Corniferous lime- stone. This was the great limestone of the Devonian, just as the Niagara was of the Upper Silurian, and the Trenton lime- 138 PALEOZOIC TIME. stone of the Lower Silurian. It spreads through New York from the Helderberg Mountains south of Albany, where it has been called the Upper Helderberg limestone; and stretches westward to the Mississippi, and beyond it into Iowa and Missouri. In New York and along the Appalachian region, it is underlaid by a sandstone or grit rock. The limestone is in some places a coral-reef rock, as plainly so as any coral-reef limestone in modern tropical seas. Near Louisville, Kentucky, at the Ealls of the Ohio, it consists of an aggregation of corals, many of large size, and some are standing in the position of growth. The limestone rock often contains a kind of flint called hornstone; and, as the Latin for horn is cornu, the limestone was named the Corniferous limestone. The Devonian deposits following this limestone called often the Upper Devonian are mostly sandstones and shales, named the Hamilton, Portage, and Chemuug beds, from locali- ties in New York ; and above these, at the top, there is an extensive conglomerate and sandstone called the Catskill group. These fragmental formations are confined mainly to Southern New York and to the Appalachian region to the southwest. In parts of the Interior region there were limestones form- ing when the Hamilton sandstones and shales were in pro- gress; but subsequent to these limestones the Devonian rock formed in the Interior region is mainly a shale of little thickness. DEVONIAN AGE. 139 The flagging-stone so much used in New York and the adjoining States is an argillaceous sandstone from the Hamil- ton beds at Kingston and other places on the Hudson Eiver. In Great Britain the Devonian formation includes a great thickness of red sandstone in Scotland, Wales, and England, which was formerly distinguished as the " Old Red Sandstone/'' In South Devon there are limestone and shales in place of red sandstone, and hence a greater abundance of fossils. In the Eifel, Germany, the Eifel limestone is a Devonian coral- reef rock of the age of the Corniferous. Devonian sandstones cover a large area in Eussia. 2. Life. 1, Plants. The plants included, besides sea-weeds, various terrestrial kinds; and among them, in the middle and later Devonian, large forest-trees. These early species, as stated on page 131, were mostly of the higher Cryptogams. 7. Ferns, some of them Tree-ferns. A portion of one of the Ferns is shown in Fig. 131, and part of the stem of a Tree-fern in Fig. 132. 2. Equiseta. The modern Equiseta, or Horse-tails (the lat- ter term a translation of the former) have striated jointed stems, which may be pulled or broken apart easily at the articulations. The ancient species had a similar character. A portion of one of these rush-like Devonian plants is PALEOZOIC TIME. Figs. 181, 132. Ferns. Hf. .31. NeuropKris ^lymorph, j ,y, TreeJim, Caulopteris aMiqua. represented in Fig. 133. One of the articulations of the stem is shown at a b. In allusion to its reed-like character it is called a Odamit*, from the Latin calamm, a reed The plant represented in Fig. 134 is supposed by some to belong the Equ ]S etum tribe ; the word AteroilKto means star-leaf. 134 133 Fig. 133, Calamites transitionis ; 134, Asterophyllites latifolia. DEVONIAN AGE. 141 8. Lycopods. The earliest land plants, and those most char- acteristic of the world in ancient time, were the Lycopods. The little trailing Ground-Pines of our modern woods, so much used for decorating churches at Christmas-time, are examples of Ground-Pines; the close resemblance to miniature Pine-trees is the origin of this name. The earliest of the an- cient Lycopods were of small size, but some of those of the Middle Devonian were large forest- trees. Fig. 135 represents Figs. 135 - 137. Lycopods. Gymnosperms. F'g- I 3S> Lepidodendron primaevum ; 136, Sigillaria Hallii. Gymnosperm : 137, Cordaites RobbiL a part of the exterior of one of the Devonian Lycopods. The plants are called Lepidodendrids (from the Greek for scale and tree) , in allusion to a resemblance between the scarred surface and the scaly exterior of a reptile. The scars are the bases of the fallen leaves, and resemble the same on a dried branch from a spruce-tree. In the true Lepidodendrids the scars are in alternate order, as illustrated in Fig. 135. In 142 PALEOZOIC TIME. another group, called Sigillarifo, the scars are in vertical series, as in Fig. 136. 4. Phenogams, or Flowering Plants. Among the Flowering plants there were trees allied to the Yew, Spruce, and Pine, kinds having the simplest of flowers, and the seed naked in- stead of in pods. In allusion to the latter character they are called Gymnosperms, meaning having naked seeds. The flowers and fruit are usually in cone-like groups, and in allusion to the cones a large part of the species are Conifers. Fig. 137 is probably a leaf of one of the Conifers. 2. Animals. Protozoans, Radiates, Mollusks, and Articu- lates were represented by numerous species, as in the Silurian age; and among these Brachiopods were the prevailing Mol- lusks, Corals the most abundant Eadiates, and Trilobites the most common of Articulates. Three of the Corals of the coral-reef limestone (Corniferous limestone) from the Falls of the Ohio, near Louisville, are represented in Figs. 138-140. Fig. 138 represents a specimen of one of the large simple Corals, broken at both extremities. The radiating plates are seen at top. The top, when perfect, had a depression rayed with such plates, and to this the name of this ancient group of Corals, Cyathophylloid*, alludes, it coming from the Greek for cup and leaf. Some specimens of the species are nearly three inches in diameter at top and a foot long; and, when living, the polyp or flower-animal when expanded was as large as a small-sized sunflower, and probably as brilliant in color. DEVONIAN AGE. 143 Fig. 139 shows the surface of a massive coral whose polyps covered the surface like those of Fig. 14, on page 29. The other kind, Fig. 140, is one of the most common ; the structure Figs. 138 -UO. iHfcfilfeife*i 138 Polyp-Corals. Fig. 138, Zaphrantis gigantea ; 139, Phillipsastrsea Verneuili ; 140, Favosites Goldfussi. is columnar, suggesting that of a honeycomb, and hence its name, Favosites, from the Latin favus, a honeycomfi. Besides marine species there were also Insects among ter- restrial Articulates. Fig. 141 represents a wing of one of the May-flies of the Devonian world ; a gigantic species much exceeding any now known. It measured five inches in spread 144 PALEOZOIC TIME. Fig. 141. of wings. The May-flies or Ephemerae are species that live in the water during the young or larval state, and when ma- ture fly in clouds over moist places. One of the Devonian kinds could make the shrill sound of a locust. In addition to Invertebrates there were Fishes among Yer- tebrates. The remains of the Fishes are the head, teeth, large spines that formed the front margin of the fins, and also the whole body with its scales; but never the back-bone (vertebral column), as this was car- tilaginous and not bony, and hence decayed on burial. The species included are (1) Sharks; (2) Gars or Ganoids; and (3) intermediate kinds called Placoderms. 1. Sharks. The remains of the sharks are eitner the teeth, the shagreen, or hard, rough-pointed covering of the body, Fig. 142. Fin-spine of a Shark. and the large spines with which the front margin of the fins are sometimes armed. Fig. 142 represents one of the fin- spines of a shark of the Corniferous period, two thirds the full length. The shark was one of great size, as the length DEVONIAN AGE. 145 of the spine indicates. Some of the sharks had rather blunt, cutting teeth; but the most common kind, related to the liv-] ing Cestracion of Australian seas, had a pavement of bony/ pieces over the inner surface of the lower jaw, making the mouth a formidable grinding apparatus, fit for cracking Brachiopods and the like. 2. Gars or Ganoids. The Gar-pikes of the Mississippi and the Great Lakes, now a rare kind of Fish in the world, are examples of the type of Fishes that was exceedingly abundant in species in the Devonian Age. The scales of Gars are bony and shining, unlike those of ordinary modern Fishes, and to this, Agassiz's name, Ganoid (from the Greek for shining), refers. In many species the scales are set side by side with a special arrangement for interlocking at one margin after the fashion of the tiles on a roof; while in others they are put on more like shingles, or in the way common in ordinary fishes. Figs. 143, 144 represent two Figg W3 . U6> kinds of tile-like scales; and 145, the j^g^ ^ us under surface of two of the latter, showing how they are secured to one another. Figs. 146, 147 represent two specimens of the Ganoid fishes of the Devonian. The tail in Fig. 146 has a Scales of Ganoids - peculiarity that belonged to all of the ancient fishes; that is, the vertebral column extends to its extremity. In Meso- zoic and Cenozoic species and modern Gars the vertebral 146 PALEOZOIC TIME. Figs. 146, 147, Ganoids. Fig. 146, Dipterus raacrolepidotus (X '/i) ; 147, Holoptychius ; 147 a, scale of same. column stops at the commencement of the tail-fin, as in Tig. 148. Some of the Ganoids of the Middle Devonian whose re- mains have been found in Indiana and Ohio were of great size. Figs. 148, 149. 149 Ganoids. Fig. 148, tail of Thrissops ; 149, tooth of an Onychodus. One of them had jaws a foot to a foot and a half long, with teeth in the lower jaw (Fig. 149) two inches or more long. DEVONIAN AGE. 147 A Devonian fish between a Ganoid and Shark is repre- sented in Fig. 150. Fig. 150. Cephalaspis Lyellii. 3. Placoderms. Still stranger forms are those called Pla- coderms. The body of Fig. 151 is encased in bony pieces Fis?s. 151, 152. Placoderms. Fig. 151, Pterichthys Milleri (X #) ; 152, Coccosteus decipiens (X #) like that of a Turtle, and the length of the species, whose^ remains occur in Eussia and Scotland, is supposed to havey 148 PALEOZOIC TIME. been twenty to thirty feet. The term Placoderm alludes to the covering of plates, and is from the Greek for plate and skin. The teeth of Ganoids are usually very sharp. Sometimes they are small and fine, and grouped so as to make a brush- Fig. 153. like surface ; but often they are very large and stout. The material of the interior of the teeth, called den- tine, is intricately folded, and in allu- s i on to ^ passages of a labyrinth, such teeth are said to have within a labyrinthine texture. A simple form of this labyrinthine texture is represented in Fig. 153. The facts reviewed with reference to the life of the Devo- nian teach that during the progress of the age the marshes and dry land .were covered with jungles and forests; that the trees were without conspicuous flowers, and the most of them with no true flowers at all; that the seas were brilliant with living Corals, as well as Crinoids, and abounded in Bra- chiopods and Trilobites ; that they also had their great fishes, Sharks, Gars, and Placoderms. The land, too, had its swarms of Insects, and probably also its Spiders to spread their webs for the May-flies, although no relics of them have yet been found. 3. Mountain-making. The Devonian age passed quietly for the larger part of the North American continent, without any tilting of the rocks; CARBONIFEROUS AGE. 149 yet not without wide, though small, changes of level, varying the limits and depth of the Interior sea; such changes of level and of limits being indicated by the varying limits of the rocks, all of which are of marine origin. This quiet wa*s not interrupted between the Devonian and Carboniferous eras, as far as yet discovered, except to the northeast in the region of New Brunswick, Nova Scotia, and Northeastern Maine. There an upturning and flexing of the beds occurred, and, as a result, some mountain-making. The southward extension or growth of the dry land of the continent continued; and, by the close of the Devonian, the shore-line probably crossed the southern portion of what is now the State of New York, where is the southern limit of the outcropping Devonian, so that all of Canada except the southwest extension north of Lake Erie, nearly all of New York, and much the larger part of New England, were above the sea-level, together with Wisconsin and the borders of the adjoining States. There was probably also an island, trending north-northeast, over the Cincinnati region (page 135), and an- other about an Archaean area in Missouri. See map, page 105. 3. Carboniferous Age, or Age of Coal-Plants. The Carboniferous age was the time when the most exten- sive coal-beds of Europe and America were formed. The name Carboniferous is from the Latin carbon, coal. 150 PALEOZOIC TIME. 1. Rocks. Coal-measures. 1. The age commenced with a marine period, the Subcar- boniferous, in which a large part of the North American continent was under the sea, though not at great depths, and Great Britain and Europe also were to a large extent sub- merged. During it, limestone strata, with some intervening sand-beds, were in progress in portions of Great Britain and Europe, and over much of the Mississippi basin or the In- terior region; and, at the same time, great fragmental depos- its, making sandstones, shales, and conglomerates, were laid down along the Appalachian region from the borders of New York southwestward, the thickness of which was five times as V great as that of the limestone strata. The limestone was formed to a great extent of Crinoids, and has been called Crinoidal limestone. The Crinoids were of numerous species and very various forms. One of the most perfect specimens is represented in Fig 154, only the stem below being wanting. The figure shows the numberless stony pieces really blocks of limestone material of which it con- sists, and which ordinarily fell to pieces when the animal died, as there was little animal membrane to hold them together. The animal opened out its arms at will, and when expanded, the breadth of the flower-like summit in this species was about three inches. The stem below, when entire, was prob- ably a foot or more long. The little disks of which the stem CARBONIFEROUS AGE. 151 in Crinoids consists, looking like button-moulds, are common fossils in the limestones. (See page 34.) Some of them are an inch in diameter. Fig. 155 represents another kind of Crinoid, which was without_ams, called a Pentremites, from the Greek for Jive, the form of the stem being approximately five-sided. Figs. 154-156. Crinoids. Coral. Fig. 154, Zeacrinus elegans ; 155, Pentremites pyriformis. Coral : 156, surface of Lithostrotion Canadense. There were also Corals; and a top view of the most com- mon of these is represented in Fig. 156. Brachiopods also contributed largely to the rock, as to all earlier limestones : figures of two of them are given in Figs. 157, 158. 2. After the Subcarboniferous period a period of submer- gence began the true Coal period, or that of the Coal-meas- ures, as the series of coal-beds and rocks containing them is called. The rocks are mostly sandstones, shales, and conglom- ) 152 PALEOZOIC TIME. crates; but in the Interior region of North America there / are some intervening limestone strata. The rock at the base of the coal-measures is generally a conglomerate called the millstone-grit. 157 Brachiopods. Fig. 157, Spirifer bisulcatus ; 158, Productus punctatus. The Coal-beds contain only terrestrial or fresh-water fossils, and nearly all are plants; while the strata that separate them have sometimes marine or brackish water fossils. The areas of the coal-measures are the black areas on the maps of North America and England, pages 105, 114. In North America there is one area, the Acadian, to the northeast in Nova Scotia and New Brunswick; a second, of very small extent in Ehode Island; a third, the Alleghany, reaching from near the southern boundary of New York over part of Pennsylvania, Ohio, Kentucky, and Tennessee to Ala- bama ; a fourth, in Central Michigan ; a fifth, the Eastern In- terior, covering parts of Illinois, Indiana, and West Kentucky; a sixth, the Western Interior, over parts of Iowa, Missouri, CARBONIFEROUS AGE. 153 Kansas, Arkansas, and Texas. The last two were originally united in one, the Mississippi valley now separating them. It has been estimated that the area of the workable coal-beds of the United States is at least 120,000 square miles. The coal area of Nova Scotia and New Brunswick is 18,000 square miles. The principal coal areas of England are those of South Wales; the great Lancashire region east of Liverpool (B, on the map, p. 114) and Manchester (C) ; the Derbyshire coal region farther east; and on the northeastern coast, the New- castle coal-field (D). There are also coal-fields in Scotland between the Grampian range on the north and the Lammer- muirs on the south ; and others, of Ulster, Connaught, Leinster (Kilkenny), and Munster, in Ireland. The areas of England and Scotland are supposed to have been originally one great coal-field. There are valuable coal-fields of smaller extent in Belgium, Prance, and Spain, and stjll^smaller in Germany andj Southern Russia. The greatest thickness of the coal-measures in Pennsylvania^ is 4,000 feet; in Illinois, 1,200 feet; in Nova Scotia, about 15,000 feet. In Great Britian it is 7,000 to 12,000 feet in South Wales, and contains a hundred beds of coal ; 7,000 feet in Lancashire, with forty beds of coal; 2,000 feet at Newcastle. The aggregate thickness of the coal-beds of a region is not over one fiftieth, of that of the coal-measures. The coal-beds vary in thickness from less than an inch to 7* 154 PALEOZOIC TIME. 30 or 40 feet. The " mammoth vein" of the anthracite re- gion in Pennsylvania is 29 feet thick at Wilkesbarre; but there are some layers of shale in the course of it, a common fact in all coal-beds. Some coal-beds contain too much earthy matter to be of any value. The mineral coal is of different kinds. That of Central Pennsylvania and of Rhode Island is anthracite, while that of the rest of the country is almost wholly bituminous coal. Anthracite is a firm lustrous coal/ burning with but little flame, while the bituminous coal, as that from Pittsburg and the States west, is less firm and usually of less lustre, and burns with much yellow flame. The flame is due mainly to the fact that part of the carbon is combined with hydrogen (or with hydrogen and oxygen) into a compound that, when heat is applied, becomes a combustible gas or mineral oil. Bitu- minous coal when heated affords more or less of mineral oil (the material from which kerosene is obtained), although it \ contains none ; the oil or gas is produced by the heat out of some carbonaceous material present. Some bituminous coals especially those compact coals, scarcely shining, called can- ne l coa l afford 50 per cent or more of volatile matter; while anthracite yields very little, and this is mostly the vapor of water. Coals always contain some impurity which is the " ashes " and " clinkers" of a coal-fire. This ashes or earthy mate- rial was largely derived from the plants themselves, and for CARBONIFEROUS AGE. 155 the best coals wholly so; but in other cases it is part of the detritus that was from time to time washed over the beds of vegetable debris when they were forming. The coal-beds always contain a little sulphur, enough to give a sulphur smell to the gases from the burning coal; and the most of it comes from the presence of _pyrite, a compound of iron and sulphur. The layer of rock under a coal-bed is often a clayey layer, called the underclay, and it is frequently full of the under- water stems or roots of plants. The trunks sometimes project from the top of a bed of coal, as shown in Fig. 65, page 84. Many logs or great trunks lie in the strata that intervene between the coal-beds, which were once floating logs ; j and multitudes of ferns and flattened stems or trunks of these and other plants are often spread out in the shales, and espe- cially in the bed of rock directly over a coal-bed. Moreover, the coal itself, even the hardest anthracite, has sometimes im- pressions of plants in it, and, more than this, contains through- out its mass vegetable fibres in a coaly state which the microscope can detect. Coal was made from plants, and each coal-bed was origi- nally a bed of vegetable material like the peat-beds of the present time in mode of accumulation. (See, on this point, page 40.) The plant-bed having accumulated until several times thicker than the coal-bed to be made out of it, was finally covered with beds of clay or sand; and while thus buried it gradually changed to coal. 156 PALEOZOIC TIME. Plants when dried are one half carbon, the chief material of charcoal, the rest being mostly the two gases oxygen and hydrogen; after the change, eight tenths to nine tenths or more of the whole are carbon. 3. The coal-measures are followed in Europe by a series of red sandstones and clayey rocks or marlytes, with a mag- nesian limestone, constituting the Permian group, so called from the district of Perm, in Russia. In North America the Permian rocks include the sandstones and shales at the top of the coal-measures in Kansas. 2. Life. 1 Plants. The plants were similar in general character to their predecessors in the Devonian age, though mostly dif- ferent in species and partly in genera. Of the higher Cryp- togams called Acrogens (or upward growers, as the word from the Greek signifies) , because they can grow into trees there were (1) Ferns, (2) Equiseta, (3) Lycopods ; and of the Phenogams, or flowering trees, there were Conifers, or plants of the Pine-tribe. The trees and shrubs grew luxuriantly over the almost endless marshes of the continent, and spread also beyond them over the higher lands. The features of the vegetation and of the ordinary land- scape is shown in the following ideal sketch. The tree at the centre is a Tree-fern, and there are smaller Ferns below. The tree near the left side is a Lycopod of the ancient tribe CARBONIFEROUS AGE. 157 of Lepidodendrids ; and in the right corner there are other Lepidodendrids and the trunk of a Sigillaria. In the left corner there are Equiseta. The region is represented as a Fij?. 159. Carboniferous Vegetation. great marshy plain with lakes. The lakes of the Carbon- iferous era probably had their many floating islands of vege- tation, carrying large groves like the floating islands of some lakes in India. 158 PALEOZOIC TIME. Fig. 160. Fern. Sphenopteris Gravenhorstii. A portion of one of the Perns is shown in Pig. 160, and of another in Pig. 161. Pig. 162 represents one of the Equi- Fig. 161. Neuropteris hirsuta. seta, a species of Calamites (page 140) ; plants with jointed stems that grew often to a height of 20 feet, and sometimes Fig. 162. Equisetum. Calamites cannseforniis. CARBONIFEROUS AGE. 159 were a foot in diameter, very unlike the little Horse-tails of modern time. The Lycopods of the tribe of Lepidodendrids had the as- pect of Pines and Spruces, and were 40 to 80 feet or more in height. On some, the slender pine-like leaves were a foot or more long. Figs. 163, 164 show the scars of the outer 163 - 165. 163 Lycopods. Fig. 163, Lepidodendron clypeatum ; 164, Halonia pulchella ; 165, Sigillaria oculata. surface of two of the Lepidodendrids arranged, as usual, in alternate order; and Eig. 165 those of a Sigillaria in vertical series. The resemblance of the scars in the latter to an im- pression of a seal suggested the name Sigillaria y from the Latin Sigilla, seal. The cones of the Lepidodendrids and Conifers and the nuts of the latter also occur in the beds. Two of these nuts 160 PALEOZOIC TIME. are represented in Figs. 166, 167. They are supposed to have belonged to trees related to the modern yew-tree. Nearly 500 species of Carbonif- erous plants have been described from North America, and about the same number from Europe ; and of these more than one third were common to Europe and America. There are also coal-regions in the Arctic islands which have af- Nuts of conifers, forded some of the same species of Fig. 166, Trigonocarpus tricuspidatus ; 167, T.ornatus; 168, view of lower end of same. plants that W6rC growing in Eu- rope and America, showing great uniformity in the climate of the era; a fact sustained also by the occurrence in the Arctic deposits of many fossil shells and corals identical with some then living in the seas of Europe and America. 2. Animals. The seas of the Carboniferous age abounded in Crinoids and Corals among Eadiates, and Brachiopods far exceeded in number all other kinds of Mollusks; but in the group of Articulates, while there were many kinds of Worms and Crustaceans, Trilobites were few. Trilobites had been replaced by other Crustaceans, some of which were much like the modern Shrimp. Examples of the Crinoids, Corals, and Brachiopods of the earlier part of the age are figured on pages 151, 152. CARBONIFEROUS AGE. 161 Fishes were in great numbers and of large size, and they belonged to the two grand divisions that were especially char- acteristic of the Devonian, the Sharks (called also Sela- chians, from the Greek for cartilage, the Sharks being fishes with a cartilaginous skeleton) and the Ganoids. One of the Ganoids of the coal-measures is represented in Fig. 169. It Figs. 169, 170. 170, Fishes. Ganoid : Fig. 169, Eurylepis tuberculatus, from the coal-formation in Ohio. Selachian : Fig. 170, tooth of Carcharopsis Wortheni ; a, profile of section of same. has the vertebrated tail characteristic of all Paleozoic fishes. Fig. 170 shows the form and size of the teeth of one of the sharks of the Illinois region. The land had its Insects, true Spiders, Scorpions, and Cen- tipedes, and also its land Snails ; and among the Insects there were May-flies, Cockroaches, and Crickets. A view of one of the May-flies, twice the natural size, is shown in Fig. 171 ; of the wing of a Cockroach in Fig. 172; of a Spider, from Morris, Illinois, in Fig. 173; and of a Centipede, from Nova Scotia, in Fig. 174. Besides these species there were also Reptiles, the earliest 162 PALEOZOIC TIME. relics of which thus far found come from Carboniferous rocks. Footprints of them have been described from the Subcarbon- Figs. 171-174. 174 Terrestrial Articulates. Fig. 171, Miamia Bronsoni (X 2) ; 172, Blattina venusta, wing of a Cockroach. Spider : Fig. 173, Arthrolycosa antiqua. Centipede : Fig. 174, Xylobius sigillarise. iferous beds of Pennsylvania, indicating a large animal having a tail, the tail having made its mark on the mud-flat over CARBONIFEROUS AGE. 163 Fig. 175. which the animal marched. In the Carboniferous beds of Illinois, Ohio, and Nova Scotia skeletons have been found. One of them, from Ohio, is represented in Pig. 175. It has the broad cranium with large open spaces that is found in the Erog and Sala- mander; but while modern species have a naked skin and no teeth, the Carbon- iferous kinds were furnished with scales and sharp teeth very much like those of) the Ganoid fishes. Progs' and Salamanders belong to the inferior division of Rep- tiles called Amphibians. They are distinguished from true Reptiles (such as Liz- ards, Crocodiles, Snakes, Turtles) by having gills when young, which serve them for respiration until they become full grown ; then the gills drop off, and they use their lungs. The Carboniferous species are believed to have had this low fish-like character in the young state, and thus to have been related to the modern Frog and Salaman- 164 PALEOZOIC TIME. der, or Amphibians; but, while so, they were greatly superior to the modern representatives of the tribe. Besides these Amphibians, there were also true Reptiles. Fig. 176 represents a vertebra of one of them, from the Nova Scotia coal-measures. The Figs. 176, 177. . . vertebra, as the section in .big. 177 shows, was concave on both surfaces like those of fishes, and also like those of the sea-sau- rians, found in the rocks of the next geological age, reptiles Fig. I7 6, Vertebra E Acadicus, Marsh; that had paddleS like whaleS. 177, profile of same. .,, -i /> , i i -\ *> Finally, before the last period of the Carboniferous age had passed, there were also still higher Eeptiles, those that lived on the land. No remains of Birds or of Mammals have yet been found in any rocks as early as those of the Carboniferous age. 3. Changes during the Progress of the Carboniferous Age. Changes of level were going on over the North American continent throughout the Carboniferous age; but they were oscillations above and below the sea-level in many alternations, and of the gentlest and slowest kind possible, and not uplift- ings into mountains. Just such alternations of level had been in progress all through the preceding ages; but the Carbon- iferous movements were peculiar in this, that the continent CARBONIFEROUS AGE. 165 over its broad surface was just balancing itself near the wa- ter's surface, part of the time bathing in it and then out in the free air, and so on, alternately; while, in former times, the oscillations seldom carried the interior region out of the sea, or if it did, only portions at a time. It was peculiar also in the fact that the wide continent lay quiet above the sea-level, with a nearly even surface, for a very great period of time, sufficiently long to make beds of vegetable debris thick enough for coal-beds; many of the coal-beds are six feet thick, and some twenty or more ; and even six feet would ( require, according to an estimate that has been made, a bedh thirty feet thick for bituminous coal, and a much thicker one/ for anthracite. The Interior of the continent from Eastern Pennsylvania to Central Kansas was a region of vast jungles, lakes with float- ing grove-islands, and some dry-land forests, and the debris of the luxuriant vegetation produced the accumulating plant- beds. A Cincinnati area of emerged land then divided the continental marsh from Lake Erie to Tennessee; but farther^ south the eastern and western portions were probably united. J The Michigan coal area was an independent marsh region. The Green Mountains separated the Pennsylvania area from those of New England and Nova Scotia; but the two latter were probably connected along the region of the Bay of Fundy and Massachusetts Bay. The changes of level could hardly have carried up evenly 166 PALEOZOIC TIME. all parts of the Interior marsh-region from Pennsylvania to beyond the Mississippi; and it is evident that they did not, since it is difficult to make out the parallelism between the beds of the eastern, central, and western portions. The era of verdure during which a plant-bed was in pro- gress finally came to its end by a return of the salt water over the continental interior which destroyed the terrestrial life; and then began the deposition of sediment covering up the plant-beds and making sandstones or shales or conglom- erates, or the forming of limestones. Finally, the continental surface, or wide portions of it, again emerged slowly, putting an end to its marine life, and opening a new era of verdure. Such alternations continued until all the successive coal-beds were made ; some of them affecting perhaps the whole breadth of the Interior coal area, others more local. Thus the era was one of constant change ; yet change so gradual that only a being whose years were thousands or tens of thousands of our years would have been able to discover that any was in progress. In Nova Scotia the oscillations went on until nearly 15,000 feet of deposits were formed; and in that space there are 76 coal-seams and dirt-beds; and therefore 76 levels of verdant fields between the others when the waters covered the land. But over that region the waters submerging the region were mainly fresh or brackish waters, since no marine shells exist in the beds, while there are land shells and bones of reptiles. The area was an immense delta in the Carboniferous age at APPALACHIAN REVOLUTION. 167 the mouth of the St. Lawrence, then the only great river of the continent, and the submergences were connected with the floods of the stream as well as changes of level in the crust of the earth beneath. The Permian period, or the closing part of the Carbonifer- ous age, was an era of gradual submergences, without long eras of verdure or the formation of plant-beds. 4. Mountain-making at the close of Paleozoic Time. From the beginning of Paleozoic time to its close all changes over the Appalachian region west of the Archaean ridges, south- west of New England, and over the great Interior region of the continent, had gone on quietly, with gentle oscillations of the surface and slight displacements, but no general upturning in any part. These ages of quiet and regular work in rock-making were 1 very long, for Paleozoic time includes at least three fourths J V of all time after the commencement of the Paleozoic. Over the Appalachian region from New York southward, the Silurian, Devonian, and Carboniferous deposits have great thickness. The amount in Pennsylvania and Virginia has been ' estimated at 40,000 feet, or over seven miles. But over the Interior region, where limestones were the most of the time forming, the thickness is from 3,000 to 4,000 feet. These Appalachian deposits, more than ten times thicker than those of the Interior, were accumulating there for the making of a 168 PALEOZOIC TIME. range of mountains; and at the close of the Paleozoic all was ready and the mountains were made. These 40,000 feet of deposits were laid down in a great trough made by the gradual sinking of the earth's crust. Eor the lowest sandstone of the series bears evidence that it was made in shallow waters, as stated on page 116; and the last in the series, the Carboniferous beds, were spread out hori- zontally just above or just below the surface, the coal-beds proving a small emergence part of the time, and ripple-marks, mud-cracks, and footprints indicating that the sea-level was near by. The coal-measures contain beds of iron ore of great economical importance; and these are evidence that the con- dition was at times that of a great muddy marsh, probably a salt marsh, the iron ore being a marsh deposit. If, then, the top and bottom strata were made near the water-level, there must have been seven miles of sinking dur- ing the interval between their deposition. Other beds of the series bear like evidence of shallow- water origin; so that the fact is clear that the earth's crust, along what is now the region of the Alleghany Mountains, west of the Blue Ridge, for a breadth of nearly a hundred miles and a length of seven hundred and fifty or more, was slowly sinking, so slowly that the sediments laid down kept the trough all the time full to the surface, or nearly so. This sinking of the earth's crust over the region, and the concurrent accumulation of sedimentary beds, were the pre- APPALACHIAN REVOLUTION. 169 paratory steps in the mountain-making that was then to go forward, and steps that took, as above remarked, three fourths of all geological time after the Archaean era. The catastrophe consisted in the (1) folding, (2) fracturing, (3) solidifying, and in part (4) crystallizing of the beds; and also (5) in the change, in Central Pennsylvania, of bitumi- nous coal to anthracite. The folds were numerous, and involved the whole breadth of the region; and if their tops had not since been worn off by the action of water, some of the folds would now rise \ over 10,000 feet above the sea-level. Their characters are j shown in Fig. 178, of a section from Virginia, extending Fig. 178. fly # - ^yy^^^^^.x.--.^^^ from the southeast on the right to the northwest on the left, over a distance of six miles. It presents an example, as explained on page 84, of the denudation the country has undergone, as well as of the folding. The coal-formation was involved in the folds, a fact which proves that the folding began after the coal-beds were formed. Pig. 179 is a section from the vicinity of Potts- ville, Pennsylvania, P being the position of Pottsville on the coal-measures. Pig. 180 represents another from near Nes- quehoning, Pennsylvania, showing the anthracite beds doubled up, and in part vertical. 8 170 PALEOZOIC TIME. 1. The folds are steepest and most numerous to the south- eastward, or toward the ocean, and diminish to the northwest- ward. (See Fig. 178.) Figs. 179, 180. Sections of the Coal-measures. Fig. 179, on the Schuylkill, Pa. ; P, Pottsville on the coal-measures ; 14, the coal-measures ; 13 to n, Devonian formations ; 8 to 5, Upper Silurian ; 4 to 2, Lower Silurian. Fig. 180, Anthracite region, near Nesquehon- ing, Pa. ; the black lines coal-beds. 2. The folds generally have the western slope steepest, as if pressure from the direction of the ocean had pushed them westward; and sometimes the tops have thus been made to overhang the western "base. (Fig. 179.) Fig. 181. I Section of the Paleozoic Formations of the Appalachians, in Southern Virginia, between Walker's Mountain and the Peak Hills (near Peak Creek Valley). F, fault ; a, Lower Silurian limestone ; b, Upper Silurian ; c, Devonian ; d, Subcarboniferous, with coal-beds. 3. The rocks were also fractured on a grand scale, and those of the eastern side of the fracture shoved up so as to make faults in some cases of more than 10,000 feet. Fig. APPALACHIAN REVOLUTION. 171 181 represents one of these great faults. The fault is at F; to the right of F is the coal-formation, and to the left, a bent- up Lower Silurian limestone; so that a Lower Silurian rock is brought up to a level with the coal-formation, a lift, ac- cording to Lesley, of 20,000 feet. 4. The rocks were solidified through the aid of the heat caused by the movement of the rocks (page 72) ; and by the same means the change of the coal to anthracite was caused. This change to anthracite took place where the rocks are most upturned; it diminished westward, and accordingly the coal, on going west, is first a semi-anthracite or a semi- bituminous coal, and then true bituminous coal, as at Pitts- burg. The rocks in some regions were crystallized. 5. While there was so much folding and fracturing, there was no chaotic confusion of the rocks produced, the stratifi- cation being perfectly retained. It follows from the facts (1) that the force acted quietly, or with extreme slowness, for otherwise confusion would have been produced; and (2) that the pressure acted from the direction of the ocean, the forms of the folds and their greater numbers and steepness in that direction proving this. Now, what was the action producing the folding and accom- panying effects? The earth's crust below the region rested at the time on liquid rock; if it did not, the trough 7 miles in depth could not have been made by the downward bending of the 172 PALEOZOIC TIME. crust. Suppose the thickness of the crust to have been at the time 100 miles; and that below 100 miles there was fusion and the temperature of fusion. In the making of the trough the crust was bent downward, and as it formed it was kept full of sedimentary beds; so that, at the close of the Car- boniferous age, the distance from the surface to the original bottom of the bent crust was increased by 7 miles, making it 107 miles. If, then, the distance down to the temperature of fusion was 100 miles, the bottom of the. crust beneath the trough for a thickness of 7 miles must have been wholly or partly melted off. The crust would have been greatly weakened by such a loss, and also by the heat penetrating upward into it; for it had received no corresponding increase of strength from the 7 miles of deposits added, since these were not wholly consolidated. As a consequence, the pressure from the direction of the ocean, resulting from the earth's contraction (page 89), the same that had been making the trough, produced finally a break below and a collapse, and thereby a pressing together of the thick deposits lying in the trough, folding and breaking them ; and also raising the upper surface above its previous level, because the width of the base on which they rested was narrowed by the collapse. These facts respecting the formation of the Alleghany Moun- tains illustrate the way in which other mountains of folded rocks have been made. The Green Mountains had a similar history : first, a slow subsiding of the crust making a trough, APPALACHIAN REVOLUTION. 173 and a trough that was kept full of sedimentary deposits, and which took the whole of the long Lower Silurian era for its completion (probahly half the whole length of Paleozoic time) ; then a break below, and a collapse producing folds and fractures throughout the region; contemporaneously, the production of heat as a consequence of the friction of the folding and fracturing rocks, which was added to the heat that had come up into the strata from the depths below dur- ing the sinking; and the solidification and metamorphism of the various rocks as a consequence of the heat. Mountains were made in Europe and Great Britain at the same time with the Alleghanies, so that the close of Paleozoic f time has its mountain boundary elsewhere besides in America. S Changes in Paleozoic Life at the Close of the Era. In Paleozoic time Crinoids, Brachiopods, Cyathophylloid Corals, Orthocerata, Trilobites, vertebrate-tailed Ganoid Pishes, and Lepidodendrids, Sigillarids, and Calamites among plants, were characteristic species in each of the classes to which they belong. With the close of it, Trilobites, Lepidodendrids, and Sigillarids became extinct; Cyathophylloid Corals, Ortho- cerata, and vertebrate-tailed Ganoids nearly so; and, after- ward, Brachiopods among Mollusks, and Crinoids among Radiates, were greatly inferior in numbers and importance to other types of more modern character. It is thus that the Paleozoic features of the world passed by. 174 MESOZOIC TIME. The characteristics of the following era, the Mesozoic, had in part appeared before the Paleozoic era closed. Eor Am- phibians and true Eeptiles were then in existence, Shrimps and other species among Crustaceans and Insects, Spiders, and Centipedes among Articulates. And the grand division of plants which had its maximum display in the Mesozoic the Cycads, of which an account is given beyond had some species before the age closed. The extinction of species at the close of the Paleozoic was so nearly universal that, thus far, no fossils of the Carbonif- erous age have been found in rocks of later date. But the rocks now in view were those that were made over the conti- nental seas, and, more correctly, over only portions of those seas; and hence they give no facts as to the species of the ocean, and but an imperfect record of those of the continental III. Mesozoic Time. MESOZOIC TIME includes only one age, the age of Eeptiles. The Mesozoic areas on the maps of the United States and Eng- land, pages 105 and 178, are lined obliquely from the right above to the left below. Age of Reptiles. This age is divided into three periods : 1. The TRIASSIC: named from the Latin tria, three, in allusion to the fact that the rocks in Germany have three subdivisions. REPTILIAN AGE. 175 2. The JURASSIC : named after the Jura Mountains, on the eastern borders of Erance. 3. The CRETACEOUS : named from the Latin creta, chalk, the formation including the chalk-beds of England and Europe. 1. Rocks. By the close of the Paleozoic, the Interior region of the American continent east of the Mississippi had become dry land. Accordingly, Triassic and Jurassic rocks were formed only on the Atlantic border east of the Appalachians, and over the western half of the continent beyond Missouri. These rocks on the Atlantic border cover long narrow areas parallel with the Appalachians from the Gulf of St. Lawrence southwestward. One of them lies along the east side of the Bay of Fundy ; another in the Connecticut valley from Northern Massachusetts to New Haven on Long Island Sound ; another, commencing in the region of the Palisades, extends through New Jersey and Pennsylvania into Virginia; and others occur in Virginia and North Carolina. These areas are indicated on the map on page 105. The rocks are mainly red sandstones. In Virginia, near Eich- mond, and in the Deep River region, North Carolina, there are thick beds of good mineral coal. They contain no marine fos- sils ; the few that occur are either brackish-water or fresh- water. It follows, hence, that the long narrow ranges of sandstone were formed in valleys, parallel with the Appalachians, into which, for some reason, the sea did not gain full entrance. 176 MESOZOIC TIME. In Western Kansas, and farther west over the Bocky Moun- tain region, there are red sandstone strata of great extent, often containing gypsum, but generally without fossils, that are regarded as Triassic. Fossils have been found in rocks of this period in California, and also in British Columbia and Alaska. Jurassic beds, with marine fossils, overlie the Triassic of the Eocky Mountain region, west of the summit, making in part the Wahsatch Mountains, the Sierra Nevada, and other ranges. At the close of the Jurassic period a great geographical change took place in Eastern North America and also west of the Mississippi; for in the Cretaceous period beds full of marine fossils were forming all along the Atlantic border south of New York, and over a wide region bordering the Gulf of Mexico; up the Mississippi valley, to the mouth of the Ohio; from Texas northward over Kansas and a large part of the eastern slope and summit region of the Eocky Mountains, perhaps reaching to the Arctic; and also along the Pacific border west of the Sierra Nevada. The outline of the continent when these beds were in progress is shown in the accompanying map (Fig. 182), the shaded portion be- ing the part that was then under water, filled with Cretaceous life and receiving Cretaceous deposits of sediment. The Cretaceous beds are mostly soft green and gray sand- stones, partly compact shell-beds and " rotten " limestone, with hard limestone in Texas, and chalk in Western Kansas. Marine fossils are abundant, and they generally indicate shallow REPTILIAN AGE. 177 waters. Over the Bocky Mountain region the beds are in some places 10,000 feet above the sea; showing that the mountains/ -p ^ |H* have been elevated to this extent since the beds were made. ' Fig. 182. North America in the Cretaceous Period. MO, Upper Missouri region. In Great Britain the Triassic beds (No. 6 on the accom- panying map, Fig. 183) were red argillaceous sandstones and clay rocks (marlytes) formed in a partly confined sea-basin. At Cheshire they contain a bed of rock-salt derived from the evapo- ration of the waters of the sea-basin. The Jurassic rocks con- sist^ below, of a limestone called the Lias (No. 7 a) ; other 8* L 178 MESOZOIC TIME. Fig. 183. Geological Map of England. The areas lined horizontally and numbered i are Silurian. Those lined vertically (2), Devonian. Those cross-lined (3), Subcarboniferous. Carboniferous (4), black. Permian (5). Those lined obliquely from right to left, Triassic (6), Lias (7 a), Oolyte (7 6), Wealden (8), Cretaceous (9). Those lined obliquely from left to right (10, n), Tertiary. A is London ; B, Liverpool ; C, Manchester ; D, Newcastle. limestones above called Oolyte (7 b), part of which is a REPTILIAN AGE. 179 coral-reef limestone, showing that there were coral-reefs in the British seas of the era ; and near and at the top of the series, fresh-water or soil beds, called the Portland dirt-bed, and the Wealden (No. 8). The oolyte is so named from the occur- rence of beds of limestone which are made of minute spheri- cal concretionary grains, of the size of the roe of a small . fish, the word coming from the Greek for egg. As the Jurassic ended there were large areas of dry land and marshes in Southeastern England. But with the commence- ment of the Cretaceous period there was a new submergence, and green and gray sand-beds were accumulated, followed by a deeper submergence and the formation of about 1,200 feet I Figs. 184-187. Rhizopods. Fig. 184, Lituola nautiloidea ; 185, Flabellina rugosa ; 186, Chrysalidina gradata ; 188, Cuneolina pavonia. of chalk, the upperjart containing flint nodules. The chalk \ consists very largely of the shells of Ehizopods, species not larger than fine grains of sand, some of which are here fig- ured, much enlarged; and since, as stated on page 34, similar beds of Rhizopods are now in progress over the bottom of the Atlantic west of Ireland, and the Sponges and some other fossils of the chalk are probably deep-water species, it is be- 180 MESOZOIC TIME. lieved that the chalk was formed at depths not less than 1,000 feet. The flint of the chalk was made from the sili- ceous Sponges, spicules of Sponges, and Diatoms of the same sea-bottom. 2. Life. L Plants, The forests of Mesozoic time contained Conifers and Tree-Ferns, like the Carboniferous, but were especially Fig. 188. Cycas circinalis (X characterized by Cycads, plants that looked like Palms, as the figure on page 180 shows, but were Gymnosperms, like -REPTILIAN AGE. 181 the Conifers. Hence the forests of the early and middle Mesozoic consisted chiefly of Tree-ferns, Conifers, and Cycads ; \ and where the Tree-ferns and Cycads predominated the aspect j) was much like that of modern groves of Palms. 189-192. Angiosperms (or Dicotyledons). Fig. 189, Leguminosites Marcouanus ; 190, Sassafras Cretaceum ; 191, Liriodendron Meekii ; 192, Salix Meekii. In the Cretaceous beds occur the first evidence of the ex- istence, in the world, of actual Palms and of plants and trees now so common, related to the Elm, Maple, and other trees with net-veined leaves, species which have the seeds in a seed-vessel, and which are therefore called Angiosperms, from 182 MESOZOIC TIME. the Greek for vessel and seed. A few leaves from the Creta- ceous of the United States are represented in Pigs. 189 to 192. The forests still had in some places their numerous Cycads; but their general character was changed, and for the first time they looked modern. 2. Animals. The Corals and other Radiates had for the most part a general resemblance to those of the present era, although all were extinct and mostly of extinct genera. The same is true of the Mollusks, and yet some kinds under these classes were especially Mesozoic in type. This is eminently true of the higher division of Mollusks, the Cephalopods. The chambered shells of this tribe, repre- sented by Orthocerata, Nautili, and some related species in the Silurian, were in vast numbers under the type of Ammonites, while there were also many Nautili. Fig. 193 repre- sents a front view and 194 a side _., _ . , , view of one of the earlier of these V J Ammonites, a Triassic species. The animal occupied the outer cham- ber of the shell, as in the Nauti- lus (Fig. 110, page 123). Fig. 193 shows the partition which was the bottom of this outer cham- ber. Around its sides there are pocket-like depressions into which the mantle of the animal descended to enable it to hold Figs. 193, 194. Cephalopod. Fig. 193, Ammonites tornatus ; 194, side view of same reduced to one half. REPTILIAN AGE. 183 on to its shell. Two other species of Ammonites are repre- sented in Eigs. 195 - 197. Fig. 196 shows the pockets in the outer chamber of 195. Pig. 197 represents a species with the outer edge unbroken and much prolonged. The pockets are depressions in the partitions at their margins. There were some Devonian and Carboniferous species, called Goniatitet, that Figs. 195 - 197. 1 9 6 Cephalopoda. Fig. 195, Ammonites Bucklandi, from the Lias ; 196, same in profile, showing outer chamber and its pockets ; 197, A. Jason, from the OSlyte. had such pockets, but the pockets were simple in outline; those of the Ammonites are very irregularly plicated within. Their complicated outline is well shown in Fig. 198, repre- senting the series along half the margin of a partition in a Cretaceous species, the shaded part a to 6 being half of the series of pockets, twice the natural size, and b 6 the middle 184 MESOZOIC TIME. r line of the back of the shell. Among the Ammonites of ** \ the Cretaceous there were species four feet in diameter. Fig. 198. Series of pockets in Ammonites placenta. Besides these there were other kinds of Cephalopods having internal shells or bones and called Belemnites. One of these, from the Cretaceous of New Jersey, is represented in Fig. 199, but, as usual with the fossils, it is imperfect, the upper slen- der part being broken off. Pig. 200 shows a side view of the bone complete, as it has been found in some species. The bone has the same relation to the animal as the pen (Fig. 202) in the modern Squid (Fig. 201), it being internal and lying in the mantle along the back; the animal of the Belemnite was much like a Squid. These Cephalopods were in great numbers in the seas, over a thousand species having been found fossil. In view of their abundance it is a remarkable fact that no Belemnite and only one Ammonite is known to have lived after the close of the Cretaceous, and we have no evidence that by the close of the first period of the Tertiary even one was living. These highest of Mollusks ' thus passed their climax during the Mesozoic era. REPTILIAN AGE. 185 The Vertebrates included not only Fishes and Beptiles, like the Carboniferous age, but also Birds and Mammals. Figs. 199-202. Cephalopoda. Fig. 199, Belemnitella mucronata, broken at top ; 200, a Belemnite with the upper part, a b, perfect ; 201, modern Calamary or squid, Loligo vulgaris ; 202, pen or internal bone of same. Fishes. Ganoids and Sharks were the prevailing kinds of the Mesozoic until the Cretaceous era, and then fishes of modern type Herring, Salmon, Perch, and the like were in 186 MESOZOIC TIME. great numbers, species that have lony and not cartilaginous skeletons, and which are therefore called Teliosts, meaning bony throughout. They include the common edible species. The Ganoids lost their tails, that is, the vertebrated char- acter of the tail-fin, in the first period of the Mesozoic. Some species had then a vertebrated tail, some half-vertebrated, and others non- vertebrated, that is, had merely a caudal fin; but after the Triassic, all were of the modern non-vertebrated type. Reptiles. Eeptiles were the dominant species of the era through all the periods. In the Triassic, the Amphibians were of great size, as shown by their footprints on the sandstones of the Connecticut val- ley and at some other localities, and also by the bones that have occasionally been found. Some of the largest of them walked as bipeds on feet that made tracks 16 to 20 inches long and nearly as broad, and with a stride of three feet, indicating a height of at least 10 or 12 feet. Pig. 203 shows the form of the impressions. The tracks of the much smaller forefeet are occasionally found, showing that this huge biped Amphibian sometimes brought them to the ground; the form is shown in Pig. 203 a. Twenty -two consecutive tracks of one of these bipeds were laid open in 1874 at one of the quarries of Portland, Connecticut. Other species have smaller tracks, and some are less than half^an inch long. Other Amphibians of the era walked on all fours. Pigs. 204, 204 a represent the tracks of a hind foot and fore foot REPTILIAN AGE. 187 of one kind, and 205, 205 a those of another, both from the Connecticut valley. Figs. 203-206. 206* Tracks of Amphibians and True Reptiles. Amphibians : Figs. 203, 203 a, Otozoum Moodii (X /') ; 204, 204 a, Anisopus Dewyanus ( X %) ; 205, 205 a, A. gracilis ( X %). True Reptile: Fig. 206, 206 a, Anomcepus scampus, a Dinosaur ( X J4). All the Amphibians, there is reason to believe, had large teeth and scale-covered bodies, like the Amphibians of the] Carboniferous age. A tooth of a related four-footed species from Europe is shown two thirds the natural size in Pig. 207. The head of the Amphibian that was thus armed was ; over 2 feet long, and three fourths as broad. There were also true Eeptiles of various kinds. One division of them, called Dinosaurs (meaning terrible lizards), had the hinder feet three-toed like those of birds. The tracks of one from the Connecticut valley sandstone is shown one-sixth the natural size in Eig. 206. They .walked usually on their hind 188 MESOZOIC TIME. legs, like bipeds, but sometimes put their forefeet down. These were four-toed. The print of the forefoot of this species is represented in Fig. 206 a. Fig. 207. There are many kinds of three-toed tracks in the Connecticut valley sandstone which have never been found associated with tracks of the forefeet; and as they have precisely the form of those of birds, they have been regarded bird- tracks. But they may have been all made by these bird-like Eeptiles. Some of the Dinosaurs of the Jurassic and Cretaceous periods better deserve the name of saurus. terrible lizards. The Megalosaur was a huge carnivorous reptile 25 to 30 feet long; the Iguanodon and Hadrosaurs were vegetable eaters, fully as large. Another division included Enaliosaurs, or the Sea-Saurians, which had paddles like whales, and were 12 to 50 feet long. Fig. 208. Ichthyosaurus communis ( X /, o)- a, one of the vertebrae. One kind, called Iclithyosaurs (meaning fish-lizards] (Fig. 208), had a short neck, a very large eye, and thin vertebrae concave REPTILIAN AGE. 189 on both sides (Fig 208 a), much resembling those of fishes. One species was 30 feet long. Another kind, called Plesiosaurs (meaning, somewhat like a lizar d), had a long snake-like neck (Fig. 209), short body, and vertebrae as long as broad. Fig. 209. Plesiosaurus dolichodeirus ( x J6 ). a, one of the vertebrae ; b, profile of same. A third division included the Mosasaurs, snake-like rep- tiles, 15 to 80 feet long, with short paddles, jaws sometimes a yard long, and the lower jaw peculiar in having an elbow- joint to fit it to be used like an arm for working the carcass > of a great beast down its enormous throat. They had power- ful teeth; one of them, about half the size of the largest, is represented in Fig. 210. Several species have been found in the Cretaceous beds of New Jersey and Kansas, along with Hadrosaurs, Dinosaurs, and other kinds. A fourth division included Crocodiles, with long slender jaws like the Gavial, the crocodile of the Ganges. 190 MESOZOIC TIME. Fig. 210. A. ^h division included flying Beptiles, called Pterosaurs (from the Greek for winged Saurian). One of them, reduced to one fourth the natural size, is represented in Fig. 211. The wing is made by the elongation of one of the fingers and the expansion of the skin from the side of the body. Some species from Kansas had an expanse of wing of 24 or 25 feet. They had the habits of "] bats. Thus the age was literally an age of Beptiles. Air, earth, and seas were all occu- pied by them, and by species of great mag- nitude, among them those of the highest grade. The Eeptilian type thus had its maximum display in Mesozoic time. Birds. A bird with its feathers has been found fossil in the Oolyte of Solenhofen, Germany; and bones of a number of birds in the Cretaceous of the United States. The Solen- hofen bird had a long tail, furnished with a row of long quills either side. A Kansas species, described by Professor Marsh, had teeth set in sockets, a striking Eeptilian character. Mammals. Bones from a few species of Mammals have been found, the earliest in the Triassic beds of Germany and North Carolina. Fig. 212 represents a jaw-bone from North Carolina. The remains of other related kinds have been found Tooth of a Mosasaur. REPTILIAN AGE. 191 in the Oolyte at Stonesfield, England, and also in the Upper Oolyte in the Purbeck beds. The species are Marsupials, Fig. 211. Pterosaur. Fig. 211, Pterodactylus crassirostris (X #). that is, mammals related to the Opossum and Kangaroo; they are peculiar in having a pouch (Marsupium, in Latin) on the under side of the body, over the breast of the mother, for Fig. 212. Dromatherium sylvcstre. receiving the young, which are born in an immature state. Nearly all modern Marsupials are confined to the continent of Australia; a few exist still in America. 192 MESOZOIC TIME. Thus all the classes of Yertebrates had, in Mesozoic time, their species, even to Birds and Mammals. As early as the / Triassic, its first period, the Amphibians passed their climax \ in numbers, size, and grade, little being afterward known of nhe huge scale-covered tribe ; and during its following periods true Reptiles had their time of greatest expansion, giving a strong Reptilian character to the Reptilian age. But the Birds and Mammals which appeared in the age were only the commencement of tribes that were to reach their fullest dis- play in later time. Both the early Birds and Mammals had marks of inferiority, and also characteristics that showed some relation to the Reptiles with which they lived. Thus the Birds had long tails, and some, at least, true teeth like Rep- tiles ; and the Mammals have been called semi-oviparous, that is, kinds whose young were in an immature state when born, approximating in this respect to the egg state, which is an example of an extreme degree of immaturity. It is also a fact of interest that among Reptiles the Dinosaurs were like birds, not only in their biped mode of locomotion, but in the special way by which they were adapted to this kind of pro- gression ; for they had the same kind of feet as birds, the same number of toes, the same number of joints to the sev- eral toes, also hollow bones in part, a somewhat similar structure in the hinder part of the skeleton to which the leg- ^ bones are articulated, and other points of resemblance. The progress in the life of the world in Mesozoic time is REPTILIAN AGE. 193 also seen in the fact, that with the opening of its third period, Sharks and Ganoids were no longer the only fishes, the mod- ern tribes having made their appearance; and, too, Conifers, Tree-ferns, and Cycads were not the only forest-trees, for al- ready Palms and Aagbspesas had added vastly to the variety fix of foliage and to the richness of the flowers and fruits. Of lines of transition from the older trees up to these Palms and AngiagpfTTVi" nothing is known. ^ The old law of change characterized the life of Mesozoic time. New fossils are found in every successive rock-stratum, and also older kinds are missed. The system of life was in course of expansion by the introduction of new species and a casting off of the old. 3. Mountain-making in Mesozoic Time. The Sierra Nevada, Wahsatch, and some other ranges of [ the western slope of the Eocky Mountains were made at the close of the Jurassic. All the strata there existing from the bottom of the Silurian to the top of the Jurassic were folded) up in the making of the Wahsatch Mountains, and probably ) in that of the Sierra Nevada. In the course of the Jurassic, or at its close, the Triassic (or Triassic and Jurassic) rocks of the Atlantic border (Con- necticut Eiver valley and elsewhere) were slowly tilted; and then occurred a great number of deep fractures, mostly par- allel in course to the direction of the areas of the sandstone, 9 M 194 CENOZOIC TIME. which opened down to a region of liquid rock; for the liquid rock came to the surface and cooled, and now constitutes many ridges, such as Mount Holyoke, Mount Tom, the Pali- sades on the Hudson, and others between Nova Scotia on the north and South Carolina. During the formation of the sandstone a slow sinking was in progress, as is proved by the footprints on the surfaces of layers and other markings, these showing that the layers originally mud-flats and sand-flats of an estuary were successively at the water-level. The sinking brought a strain on the rock-made bottom of the trough, and ended in a breaking of the crust, and thence came the ejections of trap. The trap resembles the cooled rock of most volcanoes, but is commonly much more compact. IV. Oenozoic Time. CENOZOIC TIME comprises two Ages : I. The TERTIARY, or AGE OF MAMMALS. II. The QUATERNARY, OT AGE OF MAN. I. The Tertiary, or Age of Mammals. The Tertiary age has been divided into three sections: (1) the EOCENE; (2) the MIOCENE; (3) the PLIOCENE. These terms signify, severally, (1) the dawn of recent time; (2) the less recent ; (3) the more recent. The areas of Tertiary rocks in North America and England are distinguished on the maps, TERTIARY AGE. 195 pages 105 and 114, by being lined from the left above to to the right below. 1. Rocks. In the accompanying map the white area represents the dry land of the continent in the Eocene, or early part of the Fig. 213. Hap of North America in the early part of the Tertiary Period. Tertiary. Only the borders of the Atlantic, the Gulf of Mexico, and the Pacific (the shaded portions) were covered by the sea, and over these parts Tertiary rocks were forming through marine action aided by the contributions of rivers. 196 CENOZOIC TIME. The geographical changes since the opening of the Creta- ceous period were great, as will be seen by comparing the map with that on page 177. The Eocky Mountain region was now above the sea. The rivers of the eastern part of the continent, or those contributing waters and sediment to the Atlantic, had two thirds or more of their present extent; but the Ohio and Mississippi were still independent streams, emptying together into an arm of the Mexican Gulf. The Missouri and other western streams were just beginning to be. The Mountain region but slowly emerged, and till near the close of the Tertiary there were great lakes instead of great rivers. In the Eocene the lakes occupied the Green River and other summit basins. Afterward they were farther east and west, and in the Pliocene, as Marsh states, a lake extended from Northern Nebraska to Texas. The Tertiary consequently includes, from its beginning, vast fresh-water as well as marine formations. Marine Tertiary beds of the Eocene period were formed on the Atlantic border south of New York, and on the borders of the Mexican Gulf; but Miocene only on the Atlantic bor- | der, some change of level having excluded them from the Gulf border west of Florida; and Pliocene along the coast -^( region of South Carolina, though of this there is doubt. On the Pacific border there- are marine beds, both of the Eocene and Miocene periods; the latter are most extensive. Underneath the Marine Eocene beds of the Lower Mississippi TERTIARY AGE. 197 there are Lignitic beds, that is, beds containing lignite a kind of mineral coal retaining usually something of the structure of the original wood alternating with beds that are partly marine, the whole indicating that fresh-water marshes there alternated with fresh- water lakes and salt seas ; for the Lignitic beds were once beds of vegetable debris such as are formed in marshes. Fresh-water Tertiary beds cover large areas over the Eocky Mountain summit region, and its eastern slope, as well as part of its western in Oregon and elsewhere. They were formed in and about the great lakes alluded to above. Im- mense numbers of bones of mammals and many entire skele- tons are contained in these beds, showing that the shores of these lakes were the resort of wild beasts, some of them of elephantine size. In the Green River basin and other parts of the summit region the beds are Eocene; while over the eastern slope they are mostly Miocene and Pliocene, the latter of widest extent. Underneath these fresh-water beds over the eastern slope in the region of the Upper Missouri, and far north in British America, as well as far south, there is a Lignitic formation which is partly, especially below, of brackish- water origin; and these are equivalents of the Lignitic beds below the marine Eocene of Mississippi. Over the summit region of the mountains the Lignitic formation has a thickness of sev- eral thousand feet, and instead of Lignitic beds there are val- 198 CENOZOIC TIME. uable beds of mineral coal. There are marine, brackish-water, ; and fresh-water strata in the formation, the latter mainly in the upper part. The coal-beds occur in Wyoming, Utah, and Colorado, and some of them, opened near the Pacific Bailroad, afford coal for its locomotives. These beds overlie the Cre- taceous beds conformably, and the latter also have similar coal- beds; so that the Cretaceous deposits and era here blend with the Tertiary. Moreover, a very few Cretaceous shells occur in some of the marine beds and the remains of some reptiles related to the Cretaceous Dinosaurs. The great majority of the fossils are Tertiary in aspect and genera, and they are therefore here referred to the Eocene, although regarded as Cretaceous by some geologists. These Lignitic beds and the . underlying Cretaceous were all upturned together in one - / mountain-making effort, before the fresh-water Eocene A" i of the Green Eiver basin were deposited. In Great Britain there are marine Eocene Tertiary beds in the " London basin," and next a thin Pliocene stratum, no ma- rine Miocene existing there. Over Europe and Asia the Eocene formation was widely distributed, showing that those continents, even as late as the early Tertiary, were largely under the sea. The Pyrenees, portions of the Alps, Apennines, Carpa- thians, and mountains in Asia were partly made of them. The beds in many places contain the coin-shaped foraminifers (Ehizopod shells) called Nummulites, varying from half an inch to one inch or more in diameter; and the limestone of TERTIARY AGE. 199 which some of the Egyptian pyramids are built is made up chiefly of Nummulites. One of them is shown in Fig. 214; the exterior is represented as removed from part Figt of the interior to show the cells, which were once occupied by the minute BMzopods. Some species of a related genus occur in modern coral seas. They must have been exceedingly abundant over the great continental seas of the Tertiary. Miocene beds have a thickness of several thousand feet in Switzerland (consti- tuting the Eigi and some other summits), and occur in many ( other parts of Europe; but they are limited in area com- } pared with the Eocene. Marine Pliocene beds are of still less extent, yet have a thickness in Sicily of 3,000 feet. The marine Tertiary rocks are very various in kind. The larger part are soft sand-beds, clay-beds, and shell deposits, the shells often looking nearly as fresh as those of a mod- ern beach. Others are moderately firm sandstone. There are also loose and firm limestones. The green sand called* "marl/'' used as a fertilizer, which is so characteristic of^ the Cretaceous, also constitutes beds in the Tertiary of New Jersey. The fresh-water beds are like the softer marine beds, but contain, of course, no marine shells. Part of them are quite firm; but others are easily worn by the rains. Some great areas in the Eocky Mountain region, both over the summit and the eastern slope, have been reduced in this way 200 CENOZOIC TIME. to areas of isolated ridges, towers, pinnacles, and table-topped hills, that are mostly barren, owing to the dry climate, and which are therefore called " Bad Lands," or in French (in which language the expression was first applied), " Mauvaises Terres." 2. Life. The life of the Tertiary age shows in all its tribes an ap- proximation to that of the present time. The mammals, and probably the birds, are all of extinct species. But among the plants and the lower orders of animals there were many species that still exist : in the Eocene, a small percentage ; in the Miocene, 25 to 40 per cent; and in the Pliocene, a much larger proportion. The common oyster and clam were living as far back as the Miocene era, along with a large number of shells that are now extinct species. Progress through the Tertiary era was gradual in all departments. The forests of North America were much like the modern, but with a larger proportion of warm-climate forms. Palms flourished over Europe and in England through the Eocene. In the Miocene the European species were still those of a warmer climate than the present, and included some Australian species. Even in the Arctic zone there were in the Miocene great forests of Beach, Oak, Poplars, Walnut, and Redwood (Sequoia, the genus to which the " great trees " of California belong), with Magnolias, Alders, and others. The modern aspect of the marine shells is shown in the TERTIARY AGE. 201 following figures : Figs. 215 - 219, of American Eocene spe- cies, and 220 - 223, of Miocene from the Atlantic border. Figs. 215-219. Eocene of Alabama. Fig. 215, Ostrea sellaeformis ; 216, Crassatella alta ; 217, Astarte Conradi ; 218, Cardita planicosta ; 219, Turritella carinata. This is further manifest in the following figures of fresh-water shells from the Lignitic beds of the Rocky Mountain regions, Figs. 220-223. 222 Miocene of Virginia. Figs. 220, 221, Crepidula costata ; 222, Yoldia limatula ; 223, Callista Sayana. 9* 202 CENOZOIC TIME. species which are supposed to prove that those beds are Tertiary instead of Cretaceous. To appreciate the change since Fig. 230. Shells of the Lignitic Beds. Lamellibranchs : Figs. 224, 224 a, Corbula mactriformis ; 225, Cyrene intermedia ; 226, Unio priscus. Gasteropoda : Fig. 227, Viviparus retusus ; 228, Melania Nebrascensis ; 229, Viviparus Leai. Paleozoic time, the reader should turn back to the figures of shells on pages 121 to 133. The Tertiary Vertebrates were more unlike the moderns than- the Invertebrates. Among fishes, Sharks were exceedingly abundant, and their teeth, the most enduring part of the skeleton, are very common in some of the beds; and those of one kind, pointed, tri- angular in form, were nearly as large as a man's hand. One of the smaller of these teeth is repre- sented in Fig. 230. The true Eeptiles were Crocodiles, Lizards, Snakes, gigantic and smaller Turtles, and others. Shark's tooth. Carcharodon angustidens. TERTIARY AGE. 203 Among the birds there were Owls, Woodpeckers, Cormo- rants, Eagles; and those of France included Parrots, Trogons, Flamingoes, Cranes, Pelicans, Ibises, and other kinds related to those of warm climates. The Mammals of Mesozoic time, thus far discovered, were probably all of the lower order called Marsupials; but with the opening of the Cenozoic era there were true Mammals. The Eocene beds about Paris, France, afforded to Cuvier the first specimens described ; and now they are known from all parts of the world, and from none in greater variety than from the fresh-water Tertiary region west of the Mississippi. The earliest kinds were related most nearly to the mod- Fig. 281. Tapirus Indicus, the modern Tapir of India. ern Tapir (Fig. 231), Hog, Ehinoceros, and Hippopotamus. There were also kinds between these and the Deer. All the above mentioned are Herbivores, that is, plant-eaters. There 204 CENOZOIC TIME. were also Carnivores, or flesh-eaters, related to the dog and wolf, and Monkeys related to the Lemurs. One of the Herbivores of the Bocky Mountain Eocene is the Dinoceras of Marsh, a figure of the skull of which is here given. It was nearly as large as an Elephant, but had Fig. 232. Dinoceras mirabile (X %). six horns and was somewhat related to the Ehinoceros. Fig. 233 represents the skull of one of the Miocene species, an Oreodon, which was intermediate in characters between / the Deer, Camel, and Hog. The form of a European spe- cies more like a Deer, called a XijpJwdon, is given, as re- stored by Cuvier, in Fig. 234. There were also Horses through the Tertiary; but while the modern Horse has only TERTIARY AGE. 205 one toe out of the full mammalian number five, some of the Pliocene had three toes, one large, and two too short for use; Fig. 233. Oreodon gracilis. Miocene kinds had three toes, and all usable; and the Eocene had four toes, and all usable. Fig. 234. Xiphodon gracile. 206 CENOZOIC TIME. In the Miocene and Pliocene there were Mastodons, Ele- phants, Bhinoceroses, Camels, and Monkeys over the Bocky Mountain region, besides many smaller species. The marine Tertiary of the Atlantic border has afforded, as should be r expected, but few of these species. Cattle related to the Ox have not been found in beds earlier than the Pliocene. The Mammalian type was at last extensively unfolded, its grand divisions being well represented. But the maximum , / display of the brute races took place still later, in the early \ or middle Quaternary, after Man had appeared. 3. Mountain-making. / In North America, after the deposition of the coal (or Lig- ) nitic) beds of the summit region of the Bocky Mountains, { / and of similar beds in California, there was a flexing and / upturning of the strata along with those of the Cretaceous ' beneath, which together, as has been stated, make one con- ) tinuous series, and ridges over 3,000 feet and more high V were thus made in the coast region of California, and others of greater height in Mexico, New Mexico, Colorado, and to the north. During the formation of the Lignitic beds the uplifting of the whole Bocky Mountain region above the sea was in pro- gress; for such beds of vegetable debris as they were made from show that long periods of rest above the sea alternated with shorter periods of submergence. After the epoch of up- TERTIARY AGE. 207 turning which followed, if not also contemporaneously with it, this elevation was continued, and without a return again below the sea-level. But the existence of the vast fresh-water lakes over the surface proves, as first observed by Hayden, that the rising went forward with extreme slowness, and probably with long delays at intervals; and it is quite cer- tain that the present height at least 10,000 feet in Colo- rado and Wyoming above the level in Cretaceous times, since the Cretaceous beds, full of marine fossils, are now at this height was not attained before the close of the Pliocene, if it was then. The Pyrenees, Apennines, part of the Northern Alps, and other high mountains of Switzerland, the Carpathians, and other mountains in Eastern Europe were raised thousands of feet, and the mountain regions in Western Thibet, in Asia, 16,500 feet, after the Eocene Tertiary had partly passed, and the rise perhaps began at the same time with that of the ^ Cretaceous and Lignitic mountains of the Rocky Mountain summit and the coast region of California. After the Miocene another range 2,000 to 3,000 feet in height was made along the California coast-region west of the Cretaceous range, and some disturbances took place in the Tertiary over the summit region of the Rocky Mountains. The close of the Miocene was a time of great disturbance and of mountain-making also in Europe, to the north of the j Alps, in Switzerland, and elsewhere. 208 CENOZOIC TIME. At the same time, that is, in the Miocene era, great erup- tions of igneous rocks took place over the western slope of the Rocky Mountains, covering thousands of square miles; ^-.^ and probably the deep fractures were then opened which gave / origin to the volcanoes Mount Shasta, Mount Hood, and other summits in the Cascade Range. So also along the coast of ( Ireland and of Scotland, and the Inner Hebrides to the Faroe / Islands, the eruptions were of great extent. Fingal's Cave and S the Giant' s Causeway date from this period. In each case over the Rocky Mountains the making of a mountain range was preceded, as in that of the Appalachian region (page 168), by a sinking of the earth's crust where the range was to be, and the accumulation in the trough, as it formed, of some thousands of feet of deposits. Then followed the catastrophe, as explained for the Appalachian region on page 172, causing upturnings, foldings, fractures, consolida- tion; and sometimes also a crystallization of the beds, chang- ing them to granite, gneiss, and allied rocks. Each time, after a mountain system was completed, that part of the earth's crust was too much stiffened to be the site of another sink- ing trough, and consequently the trough made later, if there was any so made, was to one side of the former. In the Tertiary the crust over the whole Rocky Mountain region had finally become so stiffened that no new trough was begun after the Miocene; and instead of a folding of the thick Mio- cene formation into a mountain range, great breaks of the QUATERNARY AGE. 209 crust took place from which floods of lavas were let loose and the lofty volcanoes were begun. 4. Climate. During Mesozoic time the Arctic zone was warm enough for great Reptiles, warm-climate species, and the British seas for coral-reefs. The close of the Cretaceous was probably an era of unusual- cold, sending cold oceanic currents from the Arctic zone; for no other cause will account for the general destruction of spe- cies that then took place over the continental seas of America, Europe, and Asia. But the Eocene era was one of warm climate again over Great Britain, for England was then a land of Palms; and Palms continued to flourish over Middle and Southern Europe during the Miocene period. Through both the Eocene and Miocene the Arctic lands were covered with forests, and hence the Arctic climate must have been comparatively warm, not colder at least than the presents climate of the Middle United States- and Northern Prussia.]' There was a cooling off with the progress of the Miocene, and by the close of the Tertiary the earth had probably its j frigid, temperate, and torrid zones, nearly as now. 2. Quaternary Age, or Era of Man. The scene of work for the Quaternary age was to a large extent widely different from that of the Tertiary and preceding 210 CENOZOIC TIME. ages; and the kind of work was equally different. With the close of the Tertiary the continent, which was begun in the nucleal V of Archsean time, was finished out very nearly to its present limits, and at its close an elevation added the Ter- tiary formation of the sea-border to the dry land. This accomplished, the Quaternary opened. Agencies were now at work over the broad surface of the continent its dry land, and not continental seas, as formerly transport- ing southward gravel and earth from regions to the north, in order to cover the hills with gravel and soil and fill the val- leys with alluvial plains. Over both Europe and America transportation went forward from the high latitudes southward, except where there were mountains sufficiently lofty to be sources of independent movements. Hills and valleys were no impediment to the great agent engaged in this immense continental system of transportation. The aid of the ocean was not needed in these movements, and was not given ex- cept to a small extent along its borders. After these great results were attained the work of the rivers went on more quietly, and finally, through this and other agencies, in connection with some change of continental level, the earth assumed slowly its present perfected condition of surface and climate. The age is divided into three periods : (1) the GLACIAL period; (2) the CHAMPLAIN period; (3) the BECENT or TEE- RACE period. QUATERNARY AGE. GLACIAL PERIOD. 1. Glacial Period. 1. Glacial Phenomena. The general facts are these: In America and Europe, over the northern latitudes, sand, gravel, stones, and masses of rock hundreds of tons in weight are found from a few miles to a hundred and more south of the region whence they were derived. This transported ma- terial is called drift, and the stones or rocks, bowlders. In North America, the region over which the transportation took place embraced the whole surface from Labrador or Newfoundland to the western borders of Iowa, and farther west for a distance not yet determined, and it reached south- ward to the parallel of 40 and in some places beyond this. In Europe it included the British Islands and Northern Eu- rope, down to the parallel of 50, where the temperature is about the same as along the parallel of 40 in North America. The direction of travel was generally to the southeastward, southward, or southwestward. - The fact and the direction of transportation have been as- certained by tracing the stones to the ledges from which they were derived. Thus bowlders of trap and red sandstone from \ i the Connecticut valley are found on Long Island, and masses 5 of granite, gneiss, quartzyte, and other rocks in New Eng- < land, to the southward or southeastward of the ledges that > afforded them. In the same manner masses of granular mar- ble have been proved to have come from a formation 50 or 7 212 CENOZOIC TIME. 100 miles to the northward of their present position. So again masses of native copper are found in Indiana and Illi- nois that were brought from the veins of native copper south of Lake Superior. The greatest distance to which bowlders have been traced has been 400 or 500 miles in Europe, 200 or 300 over Eastern North America, and 1,000 miles along the Mississippi Eiver valley, where they reach nearly to the Gulf. The masses sometimes contain 2,000 to 3,000 cubic feet, so that they compare well in size with large houses. Drift regions are also regions of extensive planings, pol- ishings, and scratchings of the rocks (Fig. 235). These Fig. 235. Drift scratches and planings. scratches may almost anywhere be found on rocks that have been recently uncovered. Yast areas are thus scoured and scratched over, and the scratches have great uniformity in direction. The bowlders also are scratched. QUATERNARY AGE. GLACIAL PERIOD. 213 Scratches and bowlders occur on top of Mount Mansfield, the highest point in the Green Mountains, 4,430 feet above 1 the sea, and at a level of 5,500 feet on the White Mountains 5 in New Hampshire; and the direction of the scratches shows that the transporting agent moved over both of these sum- . mits without finding in them any serious impediment, and M- thence continued on its way southeastward. The drift covers the mountains and hills of drift regions, and makes also a large part of the formations in the valleys. Over the hills it is unstratified drift) the sands, gravel, and stones having gone down pell-mell together ; in the ^valleys it ) ^ is stratified drift, stratified because there the sands and gravel were deposited in flowing water, which sorted some- what the material and spread it out in beds. The excava- tions in cities or villages for the cellars of houses are often made in the stratified drift, and the sands usually show a succession of beds which is evidence of the action of water. 2. Cause of the Glacial Phenomena. No known agent is adequate for transportation on so vast a scale excepting mov- ing ice. And, as Agassiz was the first to appreciate, it was glacier ice. The size of the blocks transported is no greater than is now borne along on the backs of glaciers; and the planing and scratching is just what the Alps everywhere ex- emplifies. The moraines of the glaciers, as explained on page 60, are derived in the Alps from the cliffs either side of the ice-stream, and a small part only are taken up by the abrad- 214 CENOZOIC TIME. ing surface at bottom. In the Continental glacier of the Gla- cial period, the stones, gravel, and sand were gathered from the hills over which the ice moved, for there were no cliffs or peaks projecting above the surface even in hilly New England. The White Mountains, as above stated, have scratches to a height of 5,500 feet, or to within 800 feet of the summit, and therefore were buried in the great glacier nearly to its top, and in snow, if not ice, for the rest. Tak- I ing the height at the White Mountains as a guide, the upper surface of the glacier at that point was at least 6,000 feet above the sea-level, and the thickness of the mass about 5,000 feet. Prom this region it sloped away over Southern and Southeastern New England to its place of discharge in the Atlantic. A thickness of even 2,000 feet, which is over four times that of the largest Alpine glacier, would have given great abrading power to the heavy mass. All soft or decomposed rocks would have been deeply worn away by it, and hard rocks with open joints or planes of fracture torn to pieces; and the heavily pressing, slowly moving mass would have taken the loose and loosened rock-material over the hills beneath into itself, as additional freight for transportation. / Masses of trap 500 to JLOOCLtons in weight lie along the \ elevated western border of the plain of New Haven in Con- necticut, which were gathered up from the trap hills between Meriden and Mount Tom in Massachusetts. The hills are 1,000 to 1,300 feet high, and their tops, when the masses QUATERNARY AGE. GLACIAL PERIOD. 215 were taken up, were 1,500 to 2,000 feet below the upper sur- face of the overlying glacier. A glacier moves in the direction of the slope of its upper ( surface, in spite of the slope of the surface beneath it. It is like thick pitch in this respect. If pitch were dropped indefinitely over a spot in a plain, it would spread away indefinitely; and if the surface around had a rising slope, it would fill up the basin and then keep on its course. So it is with the ice of a glacier. In order to have a southeast- ward course, a glacier must have its surface highest to the northwestward with slope southeastward; and if the snows were more abundant to the north in the Glacial era, and the melting less abundant there, than to the south, an accumula- tion to the north might have gone on that would have pro- duced movement southward. If the plain beneath the pitch had deep channels obliquely crossing it, the pitch in these channels would follow their direction, while the overlying pitch kept on its main course. So with the glacier : its lower part within the large valleys followed the directions of the valleys, as the scratches and bowlders show; while the upper portion had its usual course, the course which is indicated by the scratches elsewhere over the higher parts of the country. The cold of the era may have been mainly due to an ele- vation and extension of Arctic lands, increasing the area of Arctic land-ice; and to a partial closing, through this eleva- 216 CENOZOIC TIME. tion, of the Arctic region against the warm current of the Atlantic Ocean, the Gulf Stream, which is now a source of warmth to all of Northeastern Europe, and even Iceland, Nova Zembla, and the polar seas and lands. Other reasons for cold have been suggested, references to which will be found in large works on the subject. South America has its Glacial region, and evidences of transportation toward the equator; so that the phenomena described were not confined to only one hemisphere. Some writers suppose it to have been alternately in the two hemi- spheres. But the evidence of this does not appear to be satis- factory. The moving glacier of New England appears to have had its head in the height of land between the St. Lawrence val- ley and Hudson Bay; for the scratches diverge from this region over Eastern Maine, New Hampshire, Vermont, and New York, being in "Western New York and the region just east of Lake Huron southwest in direction. South of drift latitudes there were glaciers of great magni- tude about the higher mountains; and moraines, scratches, roches moutonnees, occur on a grand scale in many valleys of the higher ridges of the Eocky Mountains and the Sierra Nevada, as mementos of their former Glacial history. The accompanying sketch (Fig. 236) of roches moutonnees in one of the higher valleys of Colorado is repeated here from page 61, because the events indicated belong to the Glacial period. QUATERNARY AGE. GLACIAL PERIOD. 217 The roches moutonnees extend along the valley through an ascent of nearly 2,000 feet. At present there are no glaciers within 500 miles of the place. Flar 230. View on Roche-Moutonnee Creek, Colorado. In the same era a glacier in the Alps buried all Switzer- land 2,000 to 4,000 feet deep in ice, and left immense blocks > of Alpine rocks on the Jura Mountains. Depositions of earth and stones from the glacier must have been going on to some extent through the whole Glacial era. The perpetual grinding of stones against stones in a glacier makes a very fine clayey earth ; and a clay of this kind was dropped 10 218 CENOZOIC TIME. over the hills and in the valleys, making thick deposits; and as these deposits often contain large bowlders, derived likewise from the glacier, they are called bowlder-days. 2. Champlain Period. 1. Melting of the Glacier and Deposition of the Drift. The larger part of the deposition of the drift was delayed until the glacier melted. There is reason to believe that during the Glacial period the land over the northern latitudes stood at a higher level than now, and that this was one cause of the occurrence of a cold era. Whether this were so or not, the glacier was made finally to disappear through a sinking of the land over northern latitudes, which brought on a milder climate and determined, and then hastened, the melt- ing. This subsidence marks off the commencement of the Champlain period, the second period of the Quaternary. The earlier part of it was the era of the melting of the great glacier. The melting would have gone on for a long time with extreme slowness ; but when the glacier was thinned down to the last 500 to 1,000 feet, in which part of it the most of the gravel and stones were, it went forward rapidly; and then took place the pell-mell dumping of gravel and stones over the hills and valleys, with the stratification of whatever fell into the waters. At last, as the facts prove, there was an immense flood owing to the rapidity of the final melting; for the later depositions in many regions are greatly coarser than QUATERNARY AGE. CHAMPLAIN PERIOD. 219 the earlier, the finer material having been swept away down stream and into the ocean. The Mississippi valley was the outlet for the waters of the great region it now drains; and the flood during the whole Glacial period must have been great, and floating ice laden with northern stones must have often hurried off down stream to the Gulf. But at the final flood it made thick deposits on the way to the Gulf, as observed by Hilgard, and in Mississippi bowlders as large as a bushel basket are found in the beds. Icebergs thus despatched to the Mexican Gulf must have made havoc of the warm- water life; and it is therefore no occasion for surprise, as Hilgard remarks, that the sea-shore drift deposits contain no marine species of shells. The subsidence, with which the Champlain period opened, was greatest to the north, being over 500 feet on the St. Lawrence near Montreal, 400 feet on Lake Champlain, over 200 feet on the shores of Maine, and but 40 to 100 feet along Southern New England. The river-beds hence did not have even their present slope, and consequently the rivers in part be- came great lakes. For the same reason the flood waters made deposits of great breadth along the river valleys and lake re- gions, the greatest fresh- water deposits of geological history. The depth of the submergence at Montreal, on Lake Cham- plain, along the coast of Maine, and most other points on the sea-coast is proved by the occurrence of sea-shore depos- 220 CENOZOIC TIME. its full of sea-shells at the heights just stated. In the beds on Lake Champlain the bones of a whale have been exhumed, which lived in the waters of the lake in the Champlain pe- riod, when it was a great arm of the enlarged St.- Lawrence Gulf. All the rivers and lakes over the continent in the lati- tudes north of 40, and partly those south of it, have high alluvial plains at a level far above the river or lake they border; and they were made in this Champlain period when the land was below its present level. 2. Champlain Period after the melting. After the melting was completed, the rivers, though still at flood height, were more quiet in their action, and they made depositions in the river- valleys, wherever these were not already filled to the flood level, of a finer alluvium; and much of this allu- vium contains fresh-water shells, and occasional bones of quadrupeds. The amount of sand, gravel, and clay which had been dropped over the hills by the ice was immense, and it lay loose, easy to be taken up by streams the rains might make; and hence the filling of the valleys even after the ice had disappeared may have gone forward for a while with much rapidity. But the finer alluvium shows that before the Champlain period ended the flow of the larger streams was comparatively quiet. In Europe and Great Britain the Champlain period was one of subsidence over the higher latitudes, as in America, and the subsidence was greatest to the north. In Prance and QUATERNARY AGE. RECENT PERIOD. 221 Belgium the depression below the present level was 50 to j (__ 100 feet; in Southern England, 100 to 200 feet; in Northern England and Scotland, as reported by British geologists, 1,000 ( to 1,400 feet. In Sweden it was 200 at the south to 400 or