Appalachian Plateaus of northern Ohio. Near the end of Cretaceous time this peneplain was again uplifted, forming a low plateau, and the rejuvenated streams immediately set to work to dissect it. CENOZOIC ERA TERTIARY PERIOD By H. P. CUSHING Erosion of surface. The record of Tertiary time in the Cleveland district is wholly a record of erosion. The uplift of the Cretaceous peneplain seems to have been greatest toward the northeast, so that the new plateau had a tilt more to the southwest than its predecessor. But the uplift appears to have been so gradual that the streams cut down their beds as fast as the land rose and thus maintained their previous northwesterly courses. This long-continued erosion so greatly dissected the plateau that, in the Cleveland district, only the high-level tracts which are capped by the Sharon conglomerate can be considered to represent remnants or approximate remnants of its original surface. All the rest of the district had its surface considerably worn down, the new base-level was the level of the Erie Plain, and all the surface of this plain that was underlain by softer rocks was reduced to this new level, 400 feet or more beneath the level of the plateau, which is composed mainly of more resistant rocks. The present bedrock topography of the district is substantially that produced during this period-the base-leveled Erie Plain on the north and the broadly dissected plateau on the south, with wide valleys, low divides, gentle slopes, and rolling surface. Late Tertiary elevation.-Toward the end of the Tertiary period the region was again broadly elevated, and the streams sunk their valleys well below the level of the Erie Plain, many of them much below present drainage level, so that the base-level of erosion was certainly lower than the present lake level and the land was probably so high that a valley was present where Lake Erie now lies. The interval was too short to change materially other features of the topography. The rocks were deeply weathered, and the surface was mantled by a considerable thickness of soil and rock waste. During the Tertiary period the streams of northern Ohio were much larger than their modern successors, and their sources were more remote. The largest of these streams was the one that flowed northward through the present Grand River Basin and probably carried the whole Monongahela drainage. The Cuyahoga was perhaps next in size and probably carried much of the present Tuscarawas drainage to the north. The Rocky and Chagrin Rivers probably rose farther south and had greater volume than they do to-day. t QUATERNARY PERIOD By FRANK LEVERETT PLEISTOCENE EPOCH INITIATION AND STAGES OF GLACIATION Early in the Quaternary period, in what is termed the glacial epoch, a great ice sheet was developed in the northern part of the North American Continent. From a center on the Labrador Peninsula the ice extended southward into the United States, reaching as far southwest as the Mississippi River. At the maximum extension the ice also crossed the Ohio River into Kentucky near Cincinnati and at points below. (See pl. 18.) The glacial epoch was marked by several stages of glaciation, during which the ice sheets enlarged and spread southward. Between these invasions were stages of deglaciation, when the ice sheets were melted back. Three such glacial invasions of the Ohio region are known to have occurred, with two intervening stages of deglaciation, and there probably have been four glacial invasions. These are designated as follows, beginning with the oldest: Jerseyan stage of glaciation. Illinoian stage of glaciation. Sangamon to Peorian deglaciation. In the Cleveland district the drifts of two of these stages have been distinguished, but deposits of the earlier stages appear to have been largely removed by erosion or completely buried beneath the later drifts. Nearly all the drift of the Cleveland area now open to study pertains to the Wisconsin stage. Interpretations of the conditions that prevailed during the advance of the earliest ice sheets or the recession of their borders must therefore be based chiefly on conditions attending the last ice extension and the succeeding present stage of deglaciation, for conditions similar in general must have characterized the earlier stages. ADVANCE OF THE ICE Mapping the course of the terminal moraines has shown that the configuration of the margin of the ice sheet of the Wisconsin stage was lobate (pl. 18), with extensions into lowlands and recesses on the uplands. The divergence of striae toward the morainic loops also throws light upon the direction in which the ice advanced across any particular area. In the Cleveland district the striae are found on the exposed surfaces of the sandstones, the shales being too soft to retain them. From the bearings of the striae and from the distribution of the moraines, as shown in Plate 18, it will be seen that the ice that covered the Cleveland district was spreading southeastward toward an interlobate morainal tract between the Grand River lobe on the east and a shoulder of the Scioto lobe on the west.11 DEGLACIATION In the course of the melting and disappearance of the ice sheet there were oscillations of the ice front forward and backward and not a continuous shrinking of the ice. Some moraines appear to mark positions reached by the ice after a forward movement rather than pauses in the course of the retreat. Several moraines were formed before the ice border had shrunk within the limits of the Cleveland district. The Defiance moraine represents the last notable stand of the glacial front in this region. (See fig. 8.) The Euclid moraine, which has strong development eastward from this area, represents a later position of the border of the Erie lobe. HISTORY OF THE GLACIAL LAKES The long and complicated history of the glacial lakes that occupied the Huron and Erie drainage basins has been set forth in Monograph 53 of the United States Geological Survey. Only a bare outline is therefore given in this place. The relations of the several lake levels along the water front in the Cleveland district are illustrated in Figure 9. Glacial Lake Maumee.-When the ice border in the northwestern part of Ohio held the position marked by the Defiance moraine, the waters ponded in the west end of the Erie Basin discharged to the Wabash River by an outlet leading past Fort Wayne, Ind., commonly known as the Fort Wayne outlet. (See pl. 11.) This early stage of Lake Maumee did not extend eastward as far as the Cleveland district, for the ice still persisted there on all the area below the level of that lake, and Lake Cuyahoga was restricted to the part of the valley south of this area. This highest level of Lake Maumee, about 790 feet above the sea, was maintained until the melting ice on the Thumb of Michigan, west of Saginaw Bay, opened a lower outlet, through which the water was drawn down about 30 feet. At the same time the marginal waters were extended eastward, and Lake Cuyahoga and the lakes in the branches of the Rocky River were merged with Lake Maumee. It was then that the beach known as the lowest Maumee beach was formed. It is represented by Chestnut Ridge in the Berea quadrangle and associated beach deposits at about 760 feet above the sea. The location of the outlet of this lake stage is difficult to determine, because it was subsequently covered 11 Leverett, Frank, U. S. Geol. Survey Mon. 41, pp. 401-405, 1902. |