UC-NRLF QE T 38, 143, 153. Comparisons of North American and European glacial drifts, 1910, p. 299. 26. B. Shimek. Geology of Harrison and Monoria counties, la. Geol. Surv. Reports, Vol. 20, 1909, pp. 376, 378, 386. 27. H. F. Bain. Geology of Carroll county. la. Geol. Surv. Re- ports, Vol. 9, 1898, p. 91. 28 G. F. Kay. Gumbotil, a new term, in Pleistocene geology. Science new series, Vol. 44, 1916, p. 637. 29. G. F. Kay. Personal communication. 30. G. F. Kay. Some features of the Kansan drift of southern Iowa. Bull. Geol. Soc. America, Vol. 27, 1918, p. 115. 31. F. Leverett. The Illinoian glacial lobe. General aspects of Illinoian drift-sheet. Monograph U. S. Geological Survey, Vol. 38, 1899, pp. 32, 42, 183, 184. Comparison of North American and European glacial deposits, 1910, p. 299. 32. S. Calvin. Geology of Winneshiek county. la. Geol. Surv. Reports, Vol. 16, 1905, pp. 126-127. SOME PHASES OF THE PLEISTOCENE OF IOWA 57 CHAPTER V. THE PEORIAN INTERGLACIAL EPOCH. The evidence of a Peorian interglacial epoch was based first upon the presence of fossiliferous loess beneath the drift of the Shelbyville lobe of the early Wisconsin and superimposed upon a peat and muck horizon of known Sangamon age. Plate XX. Cut east of Peoria, Illinois, showing fossiliferous loess resting on Sangamon soil. (Leverett) As stated previously, Mr. Leverett has reported rather extensive deposits of peat and muck at the base of the Wisconsin drift in McHenry, Karte, DeKalb and LaSalle counties, Illinois. More recent work on the drifts in Illinois would seem to make it very doubtful whether Towan drift underlies the Wisconsin in the above areas cited by Leverett. Since the above evidence was obtained from well data, it should not be taken as proving that the soil horizon here referred to is of Peorian age. It is just as likely to be Sangamon or Yarmouth in age as Peorian. The Toronto beds have been assigned by T. C. Chamberlin to the (!) Peorian. Professor Chamberlin remarked when he introduced the term "that the grounds for correlating these deposits with the Peorian interglacial deposits of Illinois, are not strong and that further investigation may show these gounds to be erroneous." He further states "that whether the Don beds belong to the Peorian or not, it is certain 58 THE TORONTO BEDS that vegetal beds were formed in the interval of retreat between the formation of the lowan till and the Wisconsin till, and that some of these less well developed and less well known deposits must be looked to as a type of this interglacial horizon if the Toronto beds prove unreliable. Mr. Leverett in speaking of the Toronto beds questioned seriously whether they should be assigned to this horizon, as it is his opinion that there is no lowan drift represented here. The drift underlying these beds is held by Mr. Leverett to be Illinoian and not lowan. If this is true, the deposits represented by the Toronto beds must include the time allotted to both the Sangamon and Peorian interglacial epochs. It would be very difficult to determine the exact time of deposition of these beds, since they do not hold a definite stratigraphic position where the Wisconsin drift overlaps the lowan, which would be the ideal con- dition. To better understand the relation of the Toronto beds to the drift-sheets, the following theoretical diagram is here given. Figure 6. Theoretical diagram of the Toronto beds. 5. Sand, stratified and containing trees like those in number (4) Feet. 55 4. Peaty clays containing trees and other plants of a cool temperate climate 94 3. Stratified clays and sands containing leaves and trunks of trees as well as unio shells, which are now found in middle latitudes of the United States 41 2. Old bowlder clay; deposits resting on preglacial surface of the Hudson river shale (probably Illinoian) ? i. Hudson river shale Base. Beds marked (3) in the above diagram are the Don beds, and those marked (4) and (5) are called the Scarboro beds. After the deposition of the Illinoian till (2) of the above figure, a long period of erosion ensued during which time a deep valley was cut into the drift, and sixteen feet into the underlying Hudson river shale. Upon this old surface there developed a vegetation in which grew SOME PHASES OF THE PLEISTOCENE OF IOWA 59 forest trees, which, according to Professor Penhallow, were much like those found in southern latitudes, in the vicinity of Pennsyl- vania. In this old valley was deposited coarse shingle with which was mixed trunks and branches of red-cedar, elm, oak and pawpaws. Later, owing to rise of water in Lake Ontario, which was possibly due to the damming of the lake's eastern outlet by ice, a deposit of sand and gravel to the depth of sixty feet was made in the lower part of the valley. It is in these beds that A. P. Coleman found leaves, woods, and unio shells. An examination of the fossil remains by Professor Penhallow leads him to conclude that the time represented by the Don deposits was one of moderate climate for this northern region. After the formation of the Don beds, a further deeping took place, until the water level stood 150 feet higher than at the present time. Into the lake at this point flowed a large river, which, according to Professor Coleman, was the outlet of the upper lake-region of interglacial time. The rise of the lake water produced a wide, deep bay into which the river deposited its clay and sand in the form of a large delta. That the deposit was in the form of a delta is shown by the fine lamination and stratifi- cation lines throughout the deposit. In these clays (4) of figure (6) peaty material was obtained. In the sands and gravels near the top (5) of figure (6) were found fossil unio shells and beetle wings. A study of this fauna and flora by Professor Scudder, revealed a climate much cooler than is indicated by the fauna and flora of the Don beds, and one which was more like the present climate of the Ontario region of to-day. It was because of this interpretation placed upon the fossil life that Professor Coleman has interpreted these beds as representing the outwash of the advancing Wisconsin ice-sheet. During the last two years a study of the insect life of the Sangamon beds has been made by Professor Wickham of Iowa State University. The Mahomet beds are located near Mahomet, Illinois, and belong to the Sangamon interglacial epoch. By a study of the in c ect life of this horizon it becomes possible to make a comparison of two widely separated American faunas which are thought to belong to the same interglacial stage, the Sangamon. Professor Scudder recognized in the Scarboro beds 76 species of 33 genera and 8 families, and reached the conclusion that the climate of Ontario, at the time of the deposition of the beds, was similar to that found in the same region to-day, or perhaps slightly cooler, since a num- ber of the recent allies of the fossils have now a more northern habitat. Professor Wickham, in his study of the Mahomet collec- tion, found 10 determinable species belonging to seven genera and four families, these families containing as well the bulk of Scudder' s Scarboro species in the proportion of 36, 8, 19 and 12, respectively; that is, 65 species out of the 76 which Scudder de- scribes, and five of the genera, are common to both of the collec- tions but all the species appear to be quite different. Professor Wickham contends that the basis for deductions as to climate is not very broad, but is of the opinion that the presence of Carabus meander sangamon and Chlaenius plicatipennis, the general north- ern flavor of the remaining species and the entire absence of any without fairly close recent boreal allies, suggests a more rigorous climate than that found in southern Illinois at the present time. Possibfy the climatic conditions were as severe here as they were in Ontario at the date of the formation of the Scarboro beds. It is 60 LIFE OF MAHOMET AND SCARBORO BEDS known that the same genera are living in Illinois to-day, but they occur also very far to the north, extending in part, to the very shores of the Arctic ocean. It would thus seem that an account must be taken of the entire absence of anything characteristically southern. While the species described by Professor Scudder are all different from those described by Professor Wickham, they are very closely allied. The differences are not great enough to indicate any wide dissimilarity in ecological conditions nor a sep- aration by a long period of time, neither do the likenesses prove that the beds in question were synchronous. If the Sangamon was 20,000 to 100,000 years in length, and granting both beds in question were deposited during the same stage, their formation still might be separated by thousands of years, certainly long enough to bring about a differentiation in species. In making comparisons of species, when attempting to correlate widely separated geological deposits widely different lithologically and stratigraphically, we must consider also the wide separation in space of the two places in question. Professor Wickham questions whether 10 species of the Carabiddae, Dytiseidae, Staphylinidae and Chrysomelidae, taken at random in a recent Illinois bog, would all be different from 65 species of the same families collected during the same year and in similar surroundings at Toronto. Seasons may have little to do with the divergence of the character of the fossils, since the peat deposits in which the fossils are found, are forming throughout the warmer part of the year as well as the colder, so that insect remains might readily be preserved at any time. The fact that there is no evidence of intrusion of more southern types in the Mahomet beds would suggest that the deposits perhaps formed when the Illinoian glacial lobe was well advanced on its southern route, previous to a far northern recession. The conclusion reach- ed, so far as the study of the Mahomet species is concerned, is that there is no definite way of determining whether the Mahomet fauna is more closely related to the Scarboro fauna or to those of the present day. All three, Professor Wickham thinks, would be similar to a general facies. The conclusions reached from a comparative study of the faunas of two widely separated interglacial deposits, is that it is not possible to determine positively the exact time relations of the Scarboro beds, but indications point to a nearer relationship with the Sangamon interglacial epoch than with the Peorian. In attempting to arrive at a definite conclusion as to the Peorian interglacial epoch the following lines of investigation have been undertaken: (i) the amount of erosion shown by the two last drift-sheets, (2) the degree of leaching and oxidation of the Wisconsin and lowan till-sheets, (3) the amount of erosion affected on the lowan drift before the advance of the Wisconsin, (4) the outwash products of the Wisconsin border and their state of preservation as compared with similar deposits of the lowan and, (5) the study of the interglacial deposits. One of the evidences as to whether little or much time has elapsed since the deposition of a drift-sheet, is the amount of erosion that has been accomplished since the deposition of the drift. The Wisconsin drift area may be divided into two distinct regions: (i) the terminal moraine area and, (2) the interior or plain-phase area. Since the Wisconsin was a vigorous ice-sheet it built along its margin a prominent terminal moraine. This moraine is more conspicuous for marked relief in some places than SOME PHASES OF THE PLEISTOCENE OF IOWA 61 others. This terminal area may be characterized as a surface broken by knobs and depressions with no apparent attempt at any order of assemblage. Many of the depressions are large, deep, and without outlets. In these deep kettles are to be found Iowa's largest lakes. So recent has been the retreat of this ice-sheet that the carving effect of running water has in no way changed the contour of these hills. The interior plain-phase is characterized by a level surface which is broken by gentle undulating swells and compensating convexities, which give rise to numerous, shallow, undrained saucer- like depressions. So slight is the surface relief that drainage is difficult. In this area the only evidence of erosion is to be found along some of the major streams, which are still flowing in courses they occupied before the advance of the Wisconsin ice-sheet. All the larger valleys have the appearance of immaturity. The only exceptional phase of topography found within the plain-phase is the prominent hills, sometimes solitary, sometimes grouped in irregular clusters, which seem to rise out of the level plain. At first, these hills give the appearance of hills that have been formed by erosional agents, but upon closer examination they are observed to be constructional and of glacial origin. They represent the halting attitude of the ice edge in its northward recession. Excellent examples of these morainic hills may be seen in Hamilton and Wright counties. The numerous small ponds and marshes, the larger lakes associated with the terminal moraine hills, the undissected surface all testify to a surface much the same as it was after the retreat of the Wisconsin ice-sheet. In passing from the Wisconsin border to the lowan drift but little disparity in topographic evidence is noticeable (see Plate VI.). Much of the same undulatory surface effects are present only slightly exaggerated. Drainage lines are a little more pronounced, there being a tendency in places to take on the dendritic pattern. The relief in some portions of the lowan plain is as great as 50 feet. The surface of the lowan, in many places, resembles a pre- glacial topography that has been softened by a thin mantling of drift. This is quite noticeable in passing from some of the larger streams that head in the Wisconsin drift and continue their courses across the lowan. In the lowan area the valleys are large and out of all proportion to the sizes of the streams found in them. Upon closer examination it is discovered that these channels are pre- lowan in age, this fact being shown by the superposition of lowan drift over Buchanan gravels in valley bottoms. In many instances so little erosion has been accomplished by the streams since the deposition of the lowan drift in these valley bottoms that the streams have failed to cut through the thin veneer. The numerous small ponds and marshes found upon the gentle slopes of runs and draws, and in the valley bottoms and on the crests of gentle swells, the small amount of dissection of the drift plain indicate clearly no great period of erosion between the deposition of the lowan drift and the advance of the Wisconsin ice. While it is not possible always to distinguish the different drift-sheets by their color or lithological composition, it is .gener- ally more possible to tell the Wisconsin from the other till-sheets by its color. Except in restricted areas, where the Wisconsin is 62 OXIDATION AND LEACHING OF THE DRIFT more or less sandy, the drift is of a light yellow color, while the older drifts, due to a more advanced stage of weathering, are more of a brownish yellow to a reddish brown color. Its freshness is further shown by the predominance of limestone pebbles and bowlders, many of the latter showing striae as fresh as if deposited but yesterday. Granite bowlders are present and differ from those of the lowan area in size and general color, the color of the Wisconsin bowlders being prevailingly darker than those of the lowan area. Very little difference in the degree of weathering of the Wisconsin and lowan bowlders can be detected, the bowlders of the lowan showing as fresh a surface as do those of the Wisconsin. The difference in age of the lowan and Wisconsin drift-sheets is shown best by the degree of weathering. It will be seen that the depth of oxidation, figure (i) is greater for the lowan. To deter- mine the depth of leaching, auger borings were made on the two drifts, the locations for the borings being chosen where topographic conditions were similar for both drifts. The average depth of leaching shown on the Wisconsin was 1.5 feet, while the lowan showed a depth of leaching of 3.9 feet. A study of the morainal border of the Wisconsin drift where it is in proximity to the lowan drift for outwash plain evidence, failed to reveal any worthy of note. Locally there are subdued phases, but topographically they are of little importance. A type section of such outwash plains is found in sections 5, 8 and 9 of Reeve township, Franklin county. Feet. Inches. 1. Peat, muck and black soil, highly fossiliferous 2-4 2. Clay, fine textured and white in color 6-12 3. Gravel, stratified, containing pebbles which vary in size from one-fourth to one-half inches 2-4 4. Sand and clay, greenish in color, fine grained and uniform in texture 2 5. White sand, even grained and pebbleless 2 During the time that the Wisconsin ice front occupied a position to the west of the above outwash plain, an extensive lake was formed immediately in front of the ice-edge into which was washed the fine rock flour, sand and gravel. The most important outwash deposits found along the eastern border of the Wisconsin terminal moraine are kames, kame-like eskers and the valley trains. All the larger streams which issue from the morainal border are fringed with more or less continuous gravel deposits which are usually in the form of terraces in the larger valleys of the lowan drift area. In some cases these deposits may be traced for great distances beyond the morainal border, and not infrequently, they are found extending back across the terminal moraine onto the Wisconsin drift. Some of the more important deposits are to be found near Gifford, Hardin county, where the South Fork of the Iowa river joins the parent stream; at Sheffield, along Bailey's creek, Franklin county, and at Thornton, on Beaver's creek, Cerro Gordo county. The material is largely sand and gravel, and varies greatly from place to place. The gravels are largely composed of pebbles of limestone, granite, quartzite, greenstones, and quartz. As a whole SOME PHASES OF THE PLEISTOCENE O'F IOWA 63 the gravels are fresh in appearance, except where they are poorly drained. In such positions the gravel is highly iron stained. Kame-like eskers were seen in the valley of Elk Creek, sections 21, 22 and 23, Brookfield township, Worth county, and in section 24, Green township, Cerro Gordo county. The lowan gravels when compared with the Wisconsin gravels show a higher state of weathering, though not nearly so great as the difference between the Kansan and the lowan. This would seem to clearly indicate that the time between the deposition of the lowan gravels and the coming of the Wisconsin ice, was a shorter interglacial epoch than any of the former interglacial epochs. The shorter time is further emphasized by the degree of erosion shown by the lowan drift when contrasted with the erosion of the Wisconsin. That little erosion has taken place in the valleys of the lowan, bordering the Wisconsin, is shown by the fact, that in no instance have valleys of any depth been excavated in the lowan drift. On the other hand, it is found that where streams cross from the Wisconsin onto the lowan, their channels on the latter drift are for the most part in bed-rock, and are out of all propor- tion to the size of the streams found in them. It can be demon- strated clearly that the major streams are flowing in valleys that are pre-Iowan. One of the best examples is that of Lime creek. In the S.E. 1 A Sect. 35 and S. l / 2 of Sect. 36, Fertile township, Worth county, where the river flows along the northern margin of the Wisconsin drift, there is found the following interesting relations of the drift-sheets to the valley. Figure 7. Type section of Lime creek valley east of Fertile. To the north of the river is the broad flood-plain of the river with its distinct terraces covered with lowan drift. Here the Buchanan gravels can be seen, covered with lowan bowlders. To the south of the river and immediately bordering it may be seen the steep bluff reaching to a height of 90 feet. This bluff is com- posed of Kansan drift beneath, and Wisconsin drift above. A section of this bluff was taken which shows the following inter- esting facts. 64 RELATION OF THE WISCONSIN DRIFT TO THE 1OWAN Feet. 1. Sand and gravel, largely sand in the upper part, and yellowish brown color 18 2. Clay, yellowish gray, highly stained with iron along the joints and smaller fissures 2 3. Clay, grayish yellow, highly calcareous; limestone pebbles numerous , 22 4. Clay, bluish, compact, highly calcareous 40 5. Soil and muck on a bluish, compact jointed clay; contains pieces of wood and fossil shells 2 This would seem to indicate clearly that the channel of Lime creek is pre-Iowan in age and probably of post-Kansan origin. Many other streams in the lowan area bordering the Wisconsin, show this same relationship to the lowan drift. A careful and detailed investigation was made along the east- ern margin of the Wisconsin drift, where this drift is thought to overlap the lowan, to see if it were possible to find any evidence of an overlap and to discover, if possible, evidence of interglacial deposits. This border extends from the northern boundary line of Iowa, in Worth county, to Eldora, in Hardin county. Examinations of well logs, sections of the drift, and a new coal shaft, failed to reveal the presence of anything that could be positively called lowan drift, immediately underlying the Wisconsin, along this border. There were no evidences found of interglacial deposits that could be said to be Peorian in age. A further investigation of the Wisconsin drift to the west was made to determine, if possible, whether the lowan drift extended westward beneath the Wisconsin drift. Sections examined in Hardin, Hamilton, Boone and Webster counties failed to show any positive evidence of lowan drift. The result of this investigation has led to the 'following conclusions: (i) if the Peorian was of sufficient length to permit of the develop- ment of a soil and forest zone, the vigor and strength of the Wisconsin ice, when it overrode the lowan area, destroyed all evi- dence of such deposits; (2) If the Wisconsin overlapped the lowan for any great distance, all such evidence has been obliterated. This may be due to the fact that the lowan, being a thin drift-sheet, may have been incorporated with the Wisconsin drift and hence has lost its identity; (3) the only deposit that is so far recognizable as Peorian in age, is the loess. The result of the investigation has led to the following judg- ments regarding the Peorian Interglacial Epoch; I. Geologically, the Peorian was the shortest of the- inter- glacial epochs. The evidence which seems to justify such a conclu- sion is, (i) the small amount of erosion of the lowan drift between its deposition and the advance of the Wisconsin ice, (2) the great similarity of topographic evidence between the lowan and the Wisconsin, (3) the small degree of difference shown in the state of weathering of the two drift-sheets, (4) the depth of leaching of the two drifts is such as to suggest that the two drifts are not con- SOME PHASES OF THE PLEISTOCENE OF IOWA 65 temporaneous, and a comparison of the weathered state of the Wisconsin and lowan gravels shows the Wisconsin gravels to be younger than the lowan gravels, but of no such great difference as is shown between the weathered state of the Kansan and lowan gravels, (5) the time may be largely represented by the loess deposition and the small amount of oxidation and leaching that has taken place in the loess. II. The Peorian interglacial epoch is best represented by the loess deposits. Evidence seems to justify the assumption that the Peorian was a period during which conditions were favorable for the making of thick deposits of loess. That the loess is of Peorian age has been shown by, (i) its stratigraphic relations to the lowan and Wisconsin drift-sheets, (2) by the fact that where it is found to occupy a position between the Kansan and Wisconsin drift- sheets, it shows a sharp line of demarcation from the Kansan drift, often resting on Kansan gumbotil, and is found calcareous and fossiliferous from base to top. This would seem to warrant the assumption that the loess must have been deposited shortly after the withdrawal of the lowan ice and sufficiently rapid not to permit leaching and oxidation to keep pace with the accumulation, and that the Wisconsin ice must have advanced shortly after the deposition of the loess, as the zone of leaching and oxidation be- neath the Wisconsin drift is very shallow. BIBLIOGRAPHY. T. C. Chamberlin. Glacial and interglacial beds near Toronto. Jour, of Geology, Vol. 9, 1901, p. 285. ' r 14 DAY USE RETURN TO DESK FROM WHICH BORROWED EARTH SCIENCES LIBRARY This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. LD 21-40m-5,'65 (F4308slO)476 General Library University of California Berkeley <\<\ J