UC-NRLF FROM THE LIBRARY OF WILLIAM A. SETCHELL,i864-i943 PROFESSOR OF BOTANY DEPARTMENT OF THE INTERIOR -U. S. GEOLOGICAL SURVEY ,T. W. POWELL, DIRECTOR THE FORMATION OF TRAVERTINE AND SILICEOUS SINTER BY THK VEGETATION OF HOT SPRINGS WALTER HAKVEY WEED EXTRACT FROM THE NINTH ANNUAL REPORT OF THE DIRECTOR, 1887-' WASHINGTON GOVERNMENT FEINTING OFFICE 1890 B10LOY LIBRARY FORMATION OF TRAVERTINE AND SILICEOUS SINTER BY THE VEGETATION OF HOT SPRINGS. BY WALTER HARVEY WEED. 613 OOLOGY LIBRARY CONTENTS. Paga Introduction 619 Plants as rock-builders 619 Vegetation of hot waters 620 Hot springs of the Yellowstone National Park 628 Mammoth Hot Springs 628 Geological relations 629 Travertine deposits " 629 The springs and their vegetation. 630 General occurrence of the algae 631 Effect of environment 633 Description of the vegetable growth. 635 Solubility of carbonate of lime 637 Character of the hot spring waters 638 Deposition of carbonate of lime 640 Deposits of carbonate of lime due to plant life 642 Description of the deposits 645 Weathering of the travertine ~. 649 Origin of siliceous sinter 650 Upper Geyser Basin of the Firehole River 651 General description 651 Character of the hot spring waters 654 Formation of siliceous sinter 655 Algous vegetation of the hot waters 657 Algae pools and channels 658 Fibrous varieties of algous sinter 665 Rate of deposition of siliceous sinter 666 Microscopic evidence 667 Moss sinter 667 Diatom beds. 668 Nature of siliceous sinter 669 Siliceous sinters from New Zealand 672 Summary 676 615 ILLUSTRATIONS. PLATE LXXVIII. Terraced basins of Blue Springs, Mammoth Hot Springs. 628 LXXIX. Marble basins, Mammoth Hot Springs 632 LXXX. Pulpit basins, Mammoth Hot Springs 636 LXXXI. Travertine, Mammoth Hot Springs 648 LXXXII. Algae channels, Emerald Spring, Upper Geyser Basin 656 LXXXIII. Algae basin, Eftnerald Spring, Upper Geyser Basin 658 LXXXIV. Upper algae basin, Jelly Spring, Lower Geyser Basin 660 LXXXV. Middle algae basin, Jelly Spring, Lower Geyser Basin 662 LXXXVI. Stony forms, Jelly Spring, Lower Geyser Basin 664 LXXXVII. Sinter forms from algae basins 666 FlG. 52. Travertine fan, Main terrace, Mammoth Hot Springs 632 53. Coating specimens, Mammoth Hot Springs 634 54. General view of part of Upper Geyser Basin 652 55. Avoca Spring, Upper Geyser Basin 654 56. Algae forms, Lower Geyser Basin - 663 617 FORMATION OF TRAVERTINE AND SILICEOUS SINTER BY THE VEGETATION OF HOT SPRINGS. BY WALTER HARVEY WEED. INTRODUCTION. Among the many interesting natural phenomena that claim the attention of the visitor to the Yellowstone National Park, the geysers and hot springs rank first in general interest. Their novelty and beauty are sure to attract universal admiration, while the vast quan- tities of hot water that flow from the ground are convincing evidences of the nearness of internal heat. These steaming fountains and boil- ing pools are usually surrounded by snowy white borders of mineral matter deposited by the hot waters. At the Mammoth Hot Springs this consists of carbonate of lime, that forms the unique marble ter- races and pulpit basins of those springs. (PI. LXXIX.) At the Geyser basins the waters deposit silica, that forms the fretted rims of the pools and the beautifully beaded and coral-like deposits of the cones, and covers large areas of ground about the springs with a sheet of white and glaring sinter. Not only are the occurrence and the nature of these deposits such as make them of interest to every visitor, but the problem of their origin has proved to be one of the prominent features in the scientific investigation of the hydrother- mal phenomena of the park, as it has been found that such deposits are very largely due to the growth and life of a brilliant colored algous vegetation, living in the hot mineral waters. PLANTS AS ROCK-BUILDERS. A review of the various geologic agents that have built up the strata forming the earth's crust shows that living organisms have taken an important part in rock formation. The abundance of their remains in ancient as well as the most recently formed sediments shows that the corals and mollusks of all periods have been active rock-builders. The geological work executed by such forms of animal life is therefore quite apparent to the students of nature. On the contrary, the geological work of plant life has not been generally rec- ognized, partly because it is less conspicuous, and partly because the absence of organic remains in many deposits formed in this way has prevented a recognition of the true origin of the rocks. 619 620 FORMATION OF HOT SPRING DEPOSITS. It has been proved that living plants further geologic change in several ways; by promoting the disintegration and decay of existing rocks, by building up new rock formations, and, upon their death, by starting a series of changes resulting from the action of the decay- ing vegetable matter upon various mineral substances. New forma- tions are built up by living plants in two ways by the accumulation of their plant remains and by the chemical reactions resulting from the growth and life of the plants: in either case mineral matter is de- posited. Where the mineral matter preserves the form and struct- ure of the plant, as is the case with the silica forming the well-known beds of diatomaceous earth, the origin of the deposit is apparent, but in many cases no trace of plant structures can be distinguished, even when thin sections of rocks that are undoubtedly formed by plants are seen under the microscope. This is true of some marine lime- stones formed by calcareous algse, and is especially true of several classes of deposits heretofore considered to have a purely chemical origin, such as travertine, siliceous sinter, certain gypsums and iron ores. In such cases it is only by a careful study of the actual* process of formation of the deposits that we can tell with certainty their true manner of formation. This has been done in the case of the deposits formed about the hot springs and geysers of the Yellow- stone Park, and it is the purpose of the present paper to show the origin and manner of formation of these interesting mineral deposits. VEGETATION OF HOT WATERS. The presence of organic life in highly heated mineral waters is a subject of considerable interest not only to students of biology, but to geological observers as well. It shows the development of life under very adverse conditions of temperature, and affords an oppor- tunity for the study of the modifying effect of high temperatures and chemical solutions upon forms found also, in ordinary surface waters. The ability of life to withstand such extreme conditions shows the possible existence of such forms in the early history of the earth, when the crust is supposed to have been covered by highly heated mineralized water. Thus far this subject has received but little attention, and the data accessible are meager and unsatisfac- tory, this being especially true of the animal life of hot waters. The vegetation of hot springs consists entirely of various species of fresh water algae, flowerless cryptogarnic plants, closely related to the salt water algse or sea- weeds. The fresh water species are less striking and varied than the marine growths, and are generally composed of green thread-like structures of more or less slimy con- sistency. ' It is well known that algae are abundant in the hot waters of many and widely separated localities, for, in the various works of 'Phycology: Prof. Farlow, in Johnson's Encyclopedia. WEED.] VEGETATION OF HOT WATERS. 621 i travel and exploration in which the occurrence of hot springs has been described, mention is frequently made of bright green confervas living in the hot pools and streams. Where the plants present in thermal waters are of this color their vegetable nature seems to have been readily recognized, but there is reason to believe that the exist- ence of algae of other colors, such as the red and yellow species com- mon in the Yellowstone springs, has generally been overlooked or the growth mistaken for mineral matter. This is not surprising, as the plants are often incrusted and hidden by mineral material de- posited by the hot water, and the organic nature of the substance is often scarcely recognizable even by botanists. Thus in sulphur waters the algae are very generally incrusted by grains of sulphur, or are inclosed in gypsum, while the vegetation of calcareous springs is often buried in travertine deposited by the water, only the grow- ing tips of the plants being free. Similarly, the threads of algae liv- ing in ferruginous waters are incrusted by oxide of iron, while in siliceous waters such growths are inclosed in gelatinous silica. In reviewing the literature of this subject, vegetation is found to be a common accompaniment of thermal springs in all parts of the world, but, although the presence of these hot-water growths has. been recognized, the conditions under which they exist are rarely given and the plants themselves have been studied and identified at very few localities. Of these the foremost is Carlsbad, Bohemia. Its hot springs have long been noted for their curative properties, and thus they attracted the attention of scientific men at an early date. In 1827, Agardth described the algous growths of these ther- mal waters, 1 and the botanist Corda 2 figured and described species from these springs in 1835. Schwabe published a paper in 1837 3 in which he describes the occurrence of the algae, giving the tempera- tures at which the different species were found, besides figuring and describing the plants themselves. The most important paper, from a geological stand-point, is, however, that published by Prof. Ferd. Cohn in 1862, 4 in which the physiological action of the plant life is shown to cause the deposition of travertine by the hot waters. Algae from the hot springs of Italy were described by Meneghine * in 1842, and Ehrenberg says' that algae occur in the hot springs of Ischia at 174 F. to 185 F. Hoppe Seyler 7 found similar vegetation in the hot waters of Lipari at 127 F. The writings of Kiitzing mention a number of species from European hot springs, and other localities are given by Rubenhart. 8 The hot springs and geysers of Iceland have been famous for many centuries, but a careful examination of the writings of the 1 Flora, 1827. 5 Monographia Nostochinarum Italica- 2 Almanach de Carlsbad, 1835-'36. rum : Turin, 1842. 3 Linnaea, 1837. Sachs in Flora, 1864. 4 Abhandl. Schles. Gesell. Naturvviss., 7 Pflugers Archiv, 1875. Heft 2, 1862. 8 Flora Aquge Dalcis. 622 FORMATION OF HOT SPRING DEPOSITS. numerous travelers who have visited and described them shows that only three authors have mentioned the presence of algous vege- tation in the hot waters. Sir William Hooker, 1 who visited Iceland in 1809, found confervas at the borders of many of the hot springs, where the plants were exposed to the steam and heat of the boiling water. Confervas limosa Dillw. was found in abundance, forming large dark-green patches attached to a coarse white clay, from which it could be easily peeled off. A brick-red confervse, an Oscillatoria, occurred in a similar way, forming large patches several inches square. Confervce, flavescens Roth, and a species allied to C. rivu- laris, were abundant in wator of a very great degree of heat. Baring-Gould, who visited the geysers in 1864, found a crimson algae growing in the spray and overflow of the spring Tunguhver.* He collected specimens, which were examined by Rev. J. M. Berk- ley, who referred them to the genus Hypheothrix, common in hot waters all over the world. Lauder Lindsay found two kinds of con- fervas in the springs of Laugarnes, Iceland, in water so hot that an egg was boiled in it in four to five minutes. 3 In New Zealand the presence of algae in the hot springs'on the south shore of Lake Taupo was first noted by Hochstetter, who says 4 the dark emerald-green growth covered the ground where the warm water flowed. The specimens collected by him are described in the Botany of the Novara Expedition. Algse from these springs are also described by W. I. Spenser,* the highest temperature of the water in which they were found be- ing 136 F. Hochstetter says the temperature of the springs varies between 125 F. and 153 F. Dr. S. Berggren, of Lund, Sweden, visited the hot spring district of New Zealand in 1874, and collected an extensive series of speci- mens of the algae of the region. He states 6 that the algaa, espe- cially Phycochromacece, but likewise Confervacece and Zygnem- acece, are to be found growing in great abundance in the .rivulets from the hot springs. These specimens have been studied by Dr. Otto Nordstedt, whose determinations show that the species are chiefly those common in hot waters in other parts of the world, and that several species occur both in hot and cold waters. Thick masses of slimy confer void plants line the bottom of a large pool, Tapui Te Koutu, at Rotorua, New Zealand, where the usual temperature is 90 to 100 F., but is 180 with a north or east wind. 7 'Journal of a Tour in Iceland, vol. 1, p. 160. 8 Iceland : Its Scenes and Sagas. 3 Bot. Zeitung, 1861, p. 859. 4 Reise der Oe. Fregatta Novara : Geol., vol. 1, pt. 1, p. 126. 5 Trans. New Zealand Inst, vol. 15, p. 302. 6 Kongl. Sv. Vet. Akademiens Handlingar, Band 22, no. 8, p. 5. 1 Skey . Mineral Waters of New Zealand Trans. New Zealand Inst. , vol. 10, p. 433. WEED.] VEGETATION OF HOT WATERS. 623 At the Azores, Mr. Mosely, naturalist on the Challenger expedi- tion, found algae growing about the hot springs of Furnas Lake, island of St. Michael. 1 The algae occur on areas splashed by the hot sulphurous waters, forming a pale, yellowish-green layer an inch and a half thick. The color is most intense in the inner layers of the growth. This gelatinous vegetable matter occurs mingled with a gray earthy material in successive layers. The temperature of the water was 176 F. to 194 F. A thick brilliant green deposit, con- sisting of Chroococcus, was found at the edge of a shallow pool of hot water whose temperature was between 149 F. and 156 F. Speci- mens were also collected from a swamp of hot mud in which, beside algse, a rush (Juncus) was found growing. The temperatures given by Mr. Mosely are all estimated, but are probably correct within the limits stated. The specimens obtained from these springs were ex- amined by Mr. W. Archer, and the result of his study published in a paper a which is mainly botanical, but is interesting in this con- nection as showing the identity of many of the species from the hot waters of the Azores, with species common in the cold waters of Great Britain. In the narrative of the voyage of the Challenger, Mr. Mosely de- scribes the occurrence of similar hot- water growths, at the Banda Islands and at the new volcano of Camiguin. At the first locality gelatinous masses of algae resembling those growing in the Azores hot springs were found around the mouths of fissures from which jets of steam issued, the only water present being that supplied by the condensation of the vapor. This sulphurous steam had a tem- perature of 250 F. within the fissure, and the thermometer stood at 140 where the algae flourished. In some places the algse and a white mineral incrustation formed alternating layers. 3 At the base of the new volcano of Camiguin two hot streams were full of algae. No vegetation was found in hot water where the tem- perature exceeded 145. 2 F., but in the stream-bed green patches oc- curred on stones projecting above the surface. As the water of this stream became cooler, a few yards farther down, algae were found growing in the middle of the channel at 113. 5 F. ''This," says Mr. Mosely, "seems to be the limiting temperature for this particular algae in this water." Where the temperature of the stream was 122 F. it fed a little side pool where algae were growing at a temperature of 101.5 F. 4 Dr. Hooker found a'gae in the hot springs of the Himalayas at several localities. ' At Soorujkoond or Belcuppec (in the Behar Hills) 1 Journ. Linn. Soc. (Bot.), vol. 14, 1875, p. 321. 2 Ibid., p. 328. 3 Voyage of H. M. S. Challenger: Narr., vol. 1, part I, p. 563. 4 Ibid, p. 654. 624 FORMATION OF HOT SPRING DEPOSITS. brown and green algae were found forming broad, luxuriant strata where the temperature did not exceed 168 F., the growth thriving until the water had cooled down to 90 F, The brown algse were found in deeper and hotter water than the green. In an appendix, Rev. J. M. Berkley, writing about the specimens collected from these springs, says a Leptothrix occurs from 80 F. to 158 F., an imperfect Zygnema between 84 F. and 112 F. 2 The same writer also describes specimens collected by Dr. Hooker from the hot springs of Momay at 110 F., and from Pugha, Thibet, in springs having a temperature of 174 F. 3 Green algous growths were observed by Prof. J. D. Dana in the hot springs of Luzon at 160 F., 4 and similar vegetation was found in the Celebes hot springs in waters of 123. 8 F. and 170 F. by Prof. A. S. Bickmore. 6 Green algous vegetation was also noted in many Japanese hot springs by Benj. Smith Lyman. 8 Cushion-shaped masses of slippery gelatinous vegetation Oscillatoria labyrinthi- formis Ach. were found by Junghuhn in the hot springs of Java 7 at 150 F., and a species of Oscillaria was found associated with a milk white precipitate of sulphate of lime at Tji-Panas. In the United States algse have been found in hot springs at many localities. Red, white, and green growths occurring in the warm sulphur springs of Virginia have given rise to the names of many of these famous resorts. 8 At the hot springs of Arkansas green cryp- togamic vegetation occurs in water having a temperature of 140 F. , and a species from this place is described by Kutzing. 9 At the so-called " geysers" of Pluton Creek, California, green algse occur in the hot acid water in great abundance. Prof. W. H. Brewer found that the highest temperature noted at which the plants were growing was 200 F., but they were most abundant in waters of 125 F. to 140 F. The growth in the hottest waters was appar- ently of the simplest kind, and composed of simple bright-green cells. Where the water had cooled to 140 F. to 149 F., bright-green fila- mentous confervas formed in considerable masses. Similar growths formed coatings on the soil about steam- jets, and were alternately exposed to very hot steam and cooler air. In a specimen collected from water having a temperature of 130 F. , Mr. A. M. Edwards, of 1 Himalayan Travels : Jos. Dalton Hooker, vol. 1, pp. 27, 379. 2 The temperatures given by Mr. Berkley are 10 lower than those given by Hooker. 3 Loc. cit., p. 379. 1 Manual of Geology, by Jas. D. Dana: 3d ed., 1880, p. 612. 5 Travels in East Indian Archipelago. "Prelim. Reports, Geol. Surv., Japan, 1874, 1877, 1879. 7 Java, Seine Gestalt, Fr. Junghuhn : vol. 2, pp. 864, 866, 868, 870, 873. 8 Geology of the Virginias, W. B. Rogers, pp. 107, 589. ' Species Algarum. WEED.] VEGETATION OF HOT WATERS. 625 New York, is said to have found animal as well as vegetable organ- isms. Professor Brewer also states that in the hot siliceous waters of Steam-boat Springs, Nevada, there is an abundant confervoid vegetation in the gelatinous mass formed where the water spreads out over the surface. This was most plentiful where the tempera- ture was about 100 F. The most interesting feature of this occur- rence is the abundant vegetation in the gelatinous silica. 5 Mr. James Blake found diatoms in water having a temperature of 163 F. at the Pueblo Hot Springs, Nevada.* The algae growing in the Benton Spring, Owen's Valley, California, are described by Mrs. Partz as representing three forms. The first is developed in the basin of the spring at a temperature of 124 F. to 135 F., the temperature of the water at the point of issue being 160 F. In the warm creek formed by the overflow of the spring the algse form waving fibers two feet long, at temperatures between 110 F. and 120 F. Below 100 F. these plants cease to grow, but a bright-green, slimy fungus occurs, disappearing as the temperature decreases. Dr. H. C. Wood gives technical descriptions of these plants, 3 and says the forms develope at the highest temperatures are immature. The presence of green confervoid vegetation in many other hot springs has been noted by various writers, but no description has been given either of the plants themselves or of the temperature and other conditions gov- , erning their occurrence. In the hot springs of the Yellowstone National Park no plant life has been found at a temperature exceeding 185 F., but at tempera- tures between 90 F. and 185 F. algous growtlis are generally pres- ent. In the reports of the Hayden Survey for 1871 and 1872 there are several references to the presence of vegetation in the hot waters. At the Mammoth Hot Springs, Dr. F. V. Hayden observed the occurrence of pale yellow filaments about the springs and the green confervoid vegetation of the waters, as well as the presence of di- atoms in the basins of the main springs, two species of the latter, Palmella and Oscillaria, being recognized by D. Billings. 4 Green vegetation was also noted in the hot waters of the Washburne, Peli- can, and Terrace Springs, and at the Lower Geyser Basin. 5 The brown leathery lining of the springs of the Lower Geyser Basin of the Firehole River was thought by Dr. Hayden to be an aggrega- tion of diatoms covered with iron oxide. 6 In 1872 Prof. F. H. Bradley recognized the presence of vegetation in the hot springs of the park, and writing of the hot waters of the Geyser Basins, says 1 Amer. Jour. Sci., 2d series, vol. 41, p. 391. 1 Manual of Geology, by James D. Dana, 3d ed., 1880, p. 611. 3 Amer. Jour. Sci., 2d series, vol. 46, p. 31. 4 Ann. Kept. U. S. Geol. and Geogr. Survey of the Territories for 1871, pp. 69,70. 5 Loc. cit., p. 136, and 1872 report, p. 55. Loc. cit, 1871, p. 105. 9 GEOL 40 626 FORMATION OF HOT SPRING DEPOSITS. that there are gelatinous forms allied to mycelium, or mother of vinegar, in nearly all the pools, except where the ebullition is so strong as to break up such tender tissues. This material occurred in broad, thick sheets of green or rusty brown, in thick, branching forms, resembling sponges, or in long waving white fibers. ' In the mucilaginous deposit on the side of a spring at the Lower Geyser Basin Dr. Josiah Curtis found skeletons of diatoms, but no living ones. Professor Bradley said the colors striping the mound of the Solitary (Lone Star) Geyser are due to purely vegetable material. His assistant, Mr. Taggart, reported leafy vegetation in springs of 120 or less at Lewis Lake, where the springs of higher temperature contained pulpy masses of a fungoid growth common about the hot springs of the Geyser Basins. 2 The botanist of the expedition, Prof. John Coulter, says in his report that algae were discovered growing in some of the hot springs. He collected orange-colored confervoid specimens from the waters of the Lower Geyser Basin which were identified by Charles H. Peck as Confervas atirantfca. 9 Prof. Theodore Comstock, who visited the park with the Jones ex. pedition in 1873, records the presence of green confervse in the Green Spring. Pelican Creek, at 104 F. , and similar growths were found at Turbid Lake, Mammoth Hot Springs, Excelsior Geyser, Sapphire Springs, and the Lake Shore Hot Springs. 4 The same observer noticed the silken yellow filaments at the Mammoth Hot Springs, and supposed the abundant "colloid matter" of the springs to originate from organic matter contained in the water, the forms being produced by the rising or buoyancy of bubbles of carbonic acid gas. 5 Dr. C. C. Parry, botanist of this expedition, noticed the presence of algse in the hot springs of the park, and says they will reward special research. 6 The report of Dr. A. C. Peale upon the thermal springs of the Yellowstone National Park 7 contains but little about the vegetation of the Park hot springs. Under the heading, " Life in Hot Springs,'* he says : At numerous places in all the geyser areas and at Gardiner's River masses of gelatinous material of greenish -red, yellow, and brown colors are noticed, and usu- ally have been considered of organic origin. In most cases where microscopical examination has been made no trace of vegetable organization has been noted, and in regions where the springs are siliceous this curious material is probably that form of gelatinous silica described in another place as viandite. In some springs of very low temperature a brown, leathery-looking material is found lining the basins. It 'Ann. Kept. U. S. Geol. and Geog. Survey of the Territories for 1872, pp. 207, 231. 2 Loc. cit., 1872, p. 250. 3 Loc. cit., p. 752. 4 Report of Reconn. N.'W. Wyoming in 1873, by Capt. Wm. Jones, U. S. War Dept., pp. 190, 194, 210, 228, 231, 238. 6 Loc. cit, p. 207. 6 Amer. Naturalist, 1874, p. 178. 'Final Rept. U. S. Geol. and Geog. Survey Terr., 1878, vol. 2, p. 359. WEED.] VEGETATION OF HOT WATEKS. 627 becomes hard upon drying, but has not as yet been examined microscopically or chemically, so that its nature is unknown, but in all probability it is one of the forms of silica rather than an organic material. This evidently represents the views of Dr. Peale and his colleagues regarding the nature of the algous growths of the Park hot springs at the time this report was prepared. This review of the literature of the subject shows how few occur- rences of hot-spring vegetation have as yet been carefully observed and described. In the cases noted, naturalists have generally given the temperature of the water in which the plants were found, and the specimens collected have been studied from a purely botanical point of view, but with the notable exception of Prof. Ferd. Cohn, observers have entirely overlooked the geological work of the lowly organized plants and the part they take in the production of hot- spring deposits. Thtse hot-water growths, like all fresh-water algae, are more widely distributed than any other plants save those peculiar to brackish waters. This is shown by the occurrence of algous vegeta- tion in the hot springs of such widely separated localities as Iceland, the Azores, New Zealand, Japan, and the United States. A com- parison of the species shows that the flora is very uniform in char- acter, being limited to a few groups and the species themselves being identical to a great extent. Perhaps the most interesting feature connected with the life of these algae is their tolerance of a high degree of heat. The extreme temperature at which vegetation has been observed is 200 F., re- corded by Prof. W. H. Brewer at the California "Geysers." On the island of Ischia, near Naples, no algse were found in hot waters above 185 F., which accords with the observations made in the Yel- lowstone National Park. At other places these growths have not been found at such high temperatures. Dr. J. D. Hooker found the limit to be 168 F. in the Himalayan springs, and Prof. Ferd. Cohn says no growths are present in the Carlsbad waters, where the tem- perature exceeds 44 R. (131 F.). As regards the effect of the chemical substances dissolved in the water there is but little known, but vegetation has been found in all varieties of water, sulphurous, calcareous, acid, and alkaline, and so far as observed the amount of material held in solution does not affect the growth. Certain species, however, are known to be peculiar to particular waters. Thus the Beggiatoce, form the characteristic vegetation of sulphur springs, and Gaillionce, are found in iron-bearing waters. The adapta- bility of particular algae to extreme conditions of environment is shown by the occurrence of the same species in the highly heated sulphurous-siliceous waters of the Azores and the cold surface waters of Great Britain. Altitude is not known to affect the growths, and algee are found 628 FORMATION OF HOT SPRING DEPOSITS. in Iceland but a few hundred feet above sea level, in the Yellow- stone National Park at 7,500 feet, and in the Himalayas at an eleva- tion of 17,000 feet. HOT SPRINGS OF THE YELLOWSTONE NATIONAL PARK. Regions of solfataric activity have always been of peculiar inter- est to scientific observers, not only on account of the curious and often extremely beautiful hot springs and the rarer occurrence of geysers in such districts, but also from the varied phenomena of rock decom- position and of mineral formation and deposition which always accompany such hydrothermal action. It is in these natural labora- tories that we are permitted to see in operation processes which have produced important changes in the rocks of the earth's crust and afford a key to many of the problems of chemical geology. There is perhaps no other district in the world where hydrother- mal action is as prominent or as extensive as it is in the Yellowstone National Park. In this area of about 3, 500 square miles, over 3, 600 hot springs and 100 geysers have been visited and their features* noted, and there are also almost innumerable steam vents. With few exceptions the hot waters are siliceous, and rise through the acidic lavas of the park, and it is probable that it is owing to this fact that the deposits formed by the hot waters do not differ more in charac- ter. The facts upon which this paper is based have been obtained in the course of a series of comparative observations carried on by the writer for the past six years at the different hot-spring areas of the Park, under the direction of Mr. Arnold Hague, geologist in charge of the Geological Survey of the Yellowstone National Park. THE MAMMOTH HOT SPRINGS. Although the Yellowstone Park abounds in hot springs, calcareous hot waters are extremely rare, and but one locality is known where such springs have formed deposits of travertine, or calcareous tufa, of any considerable extent. This is the Mammoth Hot Springs. At this place the heated waters rising through Mesozoic limestone reach the surface heavily charged with carbonate of lime in solution, which is deposited by the hot waters in the form of travertine, affording an excellent opportunity for a study of the formation of this mineral. Calcareous hot waters are not rare in nature, but are found in many parts of the world, and are usually surrounded by deposits of travertine often of considerable extent $ yet there are few places where such deposits equal those of the Mammoth Hot Springs in mag- nitude, and none exceeding them in beauty. The travertine deposits of Hierapolis in Asia Minor, famous for its hot waters in the time of the Emperor Coiistantine, form a white hill whose slopes are orna- mented with basins resembling those of the Marble Terrace of the Mammoth Hot Springs, and the springs of the Hammon Meschoutin, WEED.] TRAVERTINE DEPOSITS. 629 in Algeria, have built up cones and ridges which are the duplicate of those found on the terraces of our own locality. GEOLOGICAL RELATIONS. The Mammoth Hot Springs form the most northern of the numer- ous hot-spring areas of the Park, being situated in the northwest corner of the reservation, three-quarters of a mile south of the forty- fifth parallel, which forms the Montana- Wyoming boundary. As it is but seven miles from the terminus of the railroad it forms the first stopping place of the traveler who enters the Park from the north, and it is the most accessible of the many points of interest in this region. The situation is extremely picturesque ; the dark and lofty summit of Sepulchre Mountain rising near by on the north, while the upper valley of the Yellowstone and the sharp peaks of the Snowy Range are seen at the northeast, between the slopes of Sepulchre and the long mural face of Mount Evarts. In the southeast the eye dwells pleasingly upon the distant view of the ravine of Lava Creek and Undine Falls, with many snow-flecked peaks in the far distance. Bunsen Peak rises abruptly in the south, its dark slopes forming a pleasing background to the white mass of hot-spring deposit when seen from the north. This deposit fills an ancient ravine lying be- tween Terrace Mountain and Sentinel Butte, the grassy slopes of the latter showing exposures of Jurassic and Cretaceous limestones carved into well-defined benches by glacial action. Immediately south of the travertine terraces the sedimentary strata are covered by rhyolite, the northern extension of the great lava flows which fill the ancient basin of the Park. Near the Gardiner River, Cretaceous sandstones form small ridges, dividing the travertine sheet into three tongues ; these beds dip steeply eastward, passing beneath the strata, forming the face of Mount Evarts. TRAVERTINE DEPOSITS. The total area covered by the travertine is about two square miles, including the beds of preglacial age which form the summit of Ter- race Mountain. The greatest thickness is probably about two hun- dred and fifty feet, but the average is very much less. The upper limit of the deposit, forming the terraces and filling the ravine, is about 1,400 feet above the Gardiner River and 7,100 feet above sea level ; the travertine extends from this terrace down to the river, forming a continuous covering of varying width and thickness. It is impossible to measure the volume of the deposit as the thickness is variable, and the contour of the underlying surface can be con- jectured only by the relation of the neighboring slopes. The usual approach to the Mammoth Hot Springs from the rail- road is over the road leading up the picturesque gorge of the Gar- diner to the foot of the terraces. Recrossing this stream near its 630 FORMATION OF HOT SPRING DEPOSITS. junction with the Hot River, the road gradually ascends to the flat or terrace on which the hotels stand, 500 feet above the river. The road is built upon the hot-spring deposit, hidden on the lower slopes by drift and soil but exposed during the last 200 feet of the ascent, where many well-preserved basins may be seen on the pine and cedar covered slopes. When first seen the main mass of the recent deposit is striking from its whiteness, resembling an immense snow-bank, filling a nar- row valley whose pine-clad sides are in strong contrast to the white travertine. It has been compared by Prof. Arch. Geikie to the ter- minal front of a glacier, and by other writers to a foaming cascade suddenly turned into stone. Streaks and patches of red, yellow, and green seen upon these white slopes mark the course of the over- flowing waters, and clouds of steam float lightly upward from the springs of the main terrace and vanish in mid-air. There are in all eight well-defined benches or terraces formed by the travertine, each with a more or less level surface, and terminated by steep slopes leading to the terrace below. The largest of these flats is the Hotl. terrace, which is 83 acres in extent. This possesses several features of interest. These are usually overlooked in the desire to see the greater wonders and beauties of the upper terraces, but one can scarcely fail to notice the Liberty Cap, a pillar 43 feet in height with sphinx-like profile, the cone of a hot spring long extinct. This cone and its companion, the Thumb, with the immense empty hot- spring bowls of this terrace, attest an activity and size for these extinct springs far surpassing any now active. THE SPRINGS AND THEl^l VEGETATION. With the exception of the Hot River all the active springs now issue from the terraces above the hotels, or from the upper part of the hotel terrace itself. These seventy-five springs vary in tempera- ture from 80 F. up to 165 F., and in size from small oozes of hot water to basins 50 by 100 feet across, with an overflow of many thou- sand gallons per hour. Algae have been found in all these springs, and it is this vegetation, and the part which it takes in the forma- tion of travertine by the hot waters, that are of especial interest in the present paper. In wandering around the terraces of this great deposit of traver- tine the observer is sure to be impressed with the brightly tinted basins about the springs and the red and orange colors of the slopes overflowed by the hot waters. These colors are due to the presence of microscopic algae, which are not easily recognizable in this deposit, owing to their covering of travertine. In the cooler springs and channels similar vegetation forms the bright green, orange, or brown membrane-like sheets or masses of jelly, without apparent vegetable structure. WEED.] 'GENERAL OCCURRENCE OF THE ALG.E. 631 The true nature of the silken yellow filaments found in the bowls and channels of even the hottest springs is more apparent, though the yellow color is due to sulphur incrusting the algae threads. The intimate relation of these algous growths to the deposits of newly formed travertine suggests at once that the algae are encrusted by the carbonate of lime, and so aid in the formation of the tufa. While this is probably true, the chief work of these plants is the separation from the water of the carbonate of lime, which they cause by their abstraction of carbonic acid. Owing to this action, a common function of vegetation, such growths are an important factor in the formation of travertine by the Mammoth Hot Springs waters. GENERAL OCCURRENCE OF THE ALGJE. The general occurrence of the algous vegetation will be best un- derstood if a brief description of a few of the typical springs is given. The largest springs now active are those of the Main Terrace. This is a fairly flat area of 8f acres in extent and 250 feet above the hotels. On the north the terrace ends in abrupt slopes, extending down to the bench below ; on the east and so'utheast the descent is more gradual, extending down to the military quarters 175 feet be- low. Near the center of this terrace are the Blue Springs. These springs shift their position from year to year, the rapid deposition of travertine choking up the vents, causing the springs to seek other and easier outlets. In this case it often happens that the pressure of the accumulated gas fractures the deposit, and the water issues in a jet a foot or more in height. A rim of travertine is soon built up about the vent, forming a basin, into which the water, no w^ relieved of the excess of pressure, issues quietly, though in considerable vol- ume. The most beautiful of the Blue Springs is a pool 15 by 20 feet in extreme dimensions filled with pellucid water apparently in vio- lent ebullition. The sides and bottom of the basin are formed of pure white travertine, while the varying depths cause the water to appear all shades of blue and green, from a deep peacock blue in the deeper parts of the bowl to the lightest of Nile greens in the shallower recesses. The water, issuing with a temperature of 165 F., contains a large amount of gas, which escapes at the surface of the pool, causing the water to rise in a low dome, variations in the amount of gas producing a pulsating movement, sending out waves which ripple across the water and curl over the shallow margin of the bowl. The overflow passes over and under large fan-shaped masses of fibrous white or yellow travertine (Fig. 52) into the upper- most of a series of basins irregularly arranged in tiers, a portion running in serpentine waterways built up of travertine. These natural aqueducts are often two or three feet high. In the center is a 632 FORMATION OF HOT SPRING DEPOSITS. shallow gutter too small to hold the volume of the stream, whicK overflows the sides and fills the basins along its course. FIG. 52. Travertine fan, main terrace, Mammoth Hot Springs. These terraced overflow basins form the most striking feature of the springs. No description can do justice to their beauty, for neither the delicate fretwork of their walls nor the frosted surface of the glistening deposit, nor the brilliant colors of the pools and rims can be described. Plate LXXVIII, from a photograph, shows a few of the many basins, of which each differs from the others. The walls are built up of pure white travertine, the surface resembling imbri- cated shells or a multitude of miniature basins, and often covered with a brightly colored vegetable jelly, where the water is slightly cooled. These basin walls vary in height from a few inches to sev- eral feet. Their outline is rarely crescentic, usually irregular, wavy, and scalloped. The water runs over the rims in thin sheets and little cascades, depositing travertine wherever it flows and constantly building up the basins until the flow is checked by the increased height of the rims. Yellow sulphur-coated algse threads are abun- dant in the bowl of the spring and the rapid-flowing streams, but the exquisite blues and greens of the hottest basins are due solely to the varying depths of water. The bright lemon, red, arid green shades of the cooler pools are, however, entirely vegetable in their nature, and due to the presence of algse lining the basins and strip- ing their outer walls. In a general view of the entire collection of these basins, obtained from the edge of the terrace above, the effect is that of a brilliant mosaic, the colors occurring in well-defined areas outlined by the white travertine rims. As will be shown later, the contrasting tints of adjacent basins are due to the different tem- perature of the water and consequent different development of the algous vegetation. Looking at the pools near by proves that these colors are not pure, but are produced by a number of tints, minute differences in depth producing variations in color in the same basin. Large as is the overflow from the Blue Springs, little reaches the edge of the terrace, the water sinking into the porous deposit or flow- ing into holes and fissures in the travertine floor. On the same terrace, but close to the southeastern edge, are the WEED.] EFFECT OF ENVIRONMENT. 633 two main springs. They are very much alike, and are to-day in nearly the same condition as in 1871, when they were first seen. The northern spring is a brown lined bowl, 75 by 100 feet across, and 5 to 8 feet deep. The flat margin is formed of smooth and polished salmon-colored travertine whose thin laminse and hardness show it to have been quite slowly formed. The water is much cooler than that of the Blue Springs, having a temperature of 136 F. at the edge of the bowl. The supply is constant and issues from holes in the bottom of the basin, their location being distinguished by the lighter color of the water, the eddying currents, and an occasional stream of gas bubbles. The perfect transparency of the water enables one to see the mi- ( nutest details of the sides and bottom of the bowl. The volume of water which the two main springs pour out is not known, as the out- flow does not run in definite channels, but pours over the eastern margins in a shallow sheet which, spreading out, flows down the rippled slopes and over the Marble Basins. PI. LXXIX shows a few of the upper basins, which are often quite shallow, and hardly merit the name of basin. Here the waters deposit carbonate of lime rap- idly, and the walls or basin-fronts are generally solid, while on the lower slope the cooled waters have parted with much of their lime, and deposit travertine slowly. On these lower slopes the basins are fringed with slender stalactites and pillars, forming the beautiful Pulpit Basins, illustrated in PI. LXXX. 1 In this case, also, the pool or basin proper is very shallow, rarely a foot deep, and the rim or lip generally projects over the pillared front, as it is here that the deposition of travertine is most rapid. Wherever the hot waters fl