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been more elevated. The land wash may have come from distant Appalachia or from the Cincinnati dome, nearer at hand. The supply was intermittent, especially at first, during the Delaware epoch, but was considerably increased during the succeeding part of the Hamilton epoch. An abundant fauna swarmed in the waters and on the bottom, consisting of Hamilton forms with which are mingled survivors of the Onondaga fauna. The Onondaga forms are abundant in the Delaware, but few remain in the overlying shale of Hamil

ton age.

Portage and Chagrin sedimentation. The deposition of the beds of Hamilton age was followed by a break in the sedimentation; there was also oscillation of seas, and under the new conditions the formation of the considerable thickness of alternating black and blue shales in the Cleveland district was begun. The abundant land wash, the lack of limestone, and the high content of carbonaceous material show that the bordering lands were even more elevated than in the Hamilton epoch, that the waters were muddy and unfit for abundant life, and that during much of the time the bottom was foul with decaying organic matter. These shales are the thinned westward extension of the Portage formation of New York, and their muds were derived from lands on the north and east and perhaps also from the Cincinnati dome, though there is difference of opinion as to whether the dome was unsubmerged at this time or not. There is also difference of opinion in regard to the extent of this sea, some geologists believing that it extended west to and even over the Cincinnati dome and that these shales are the equivalent of the lower part of the Huron shale of northern Ohio and of the New Albany shale of Indiana and others, including the writer, thinking that the typical Huron is a younger formation that has nothing to do with the black shale of Portage age of the Cleveland district and that the Portage sea did not extend as far west as the Huron River. It must be left for the future to determine which of these conflicting views is true.

The black mud of the Portage sea was succeeded by the gray and blue mud of the Chagrin shale, deposited in the west end of the basin in which the Chemung rocks of New York and Pennsylvania were laid down. There was some oscillation preceding the Chagrin epoch, the bordering lands on the east were raised still higher and supplied coarser land wash to the basin of deposit, and the bottom also cleared, so that black mud ceased to be formed. In New York subsidence of the bottom of the basin was more pronounced than in the Cleveland district and conditions were more favorable for the existence of marine life, so that a much greater thickness of deposits accumulated, holding an abundant fauna from bottom to top. At Cleveland the mass of the formation is barren of fossils; the fauna did not come

into the district until near the end of the period and got no farther west at any time.

DEVONIAN OR CARBONIFEROUS SUBMERGENCE

The events that directly followed Chagrin deposition in northern Ohio are not established beyond controversy. According to one view, uplift followed the Chagrin epoch, and the entire district became a land area of low altitude and so remained for a long time, during which its surface was gently beveled off by erosion. The break is held to be the most significant one within the general series and to mark the line of division between the Devonian and Carboniferous systems. It is the writer's belief that when subsidence recommenced and deposition of the black mud of the Cleveland shale began, the marine invasion came from the south into western Ohio, where the Huron shale was deposited in a narrow bay along the east side of the Cincinnati dome. The waters slowly spread eastward, depositing the lower division of the Cleveland shale upon the Huron and farther east upon the Chagrin, and last of all laid down the upper division of the Cleveland in waters that rapidly spread farther east. Even at this greatest extent, however, the waters did not reach into Pennsylvania.

According to the other view there is no break, or none of much extent, between the Chagrin and Cleveland shales, but they are held to be deposits from the same body of water, blue Chagrin shale being deposited on the east while black Huron shale was forming at the west, and as Chagrin time went on black shale gradually spread eastward at the expense of the blue shale. The basis for this view is the fact that the blue shale grades into black shale toward the west, and the black shale is therefore held to be of late Devonian age.

Cleveland sedimentation. Deposition of the black mud of the Cleveland shale began earlier in the Berea quadrangle than in the Cleveland and slowly spread eastward. The adjacent lands were low but high enough to furnish a supply of mud to be laid down in the subsiding basin. The bottoms were foul with decaying organic matter, and the marine forms that live on the bottom and subsist on such matter were therefore absent, and their fossil remains are not found in the shales. The surface waters were purer, and life swarmed there, notably the fishes, large and small, whose remains are found in the shales.

Bedford sedimentation.-Sedimentation was interrupted at the end of the Cleveland epoch, and some warping took place in the adjacent lands, which became higher locally and capable of furnishing coarser land wash. Possibly the sea withdrew and then returned, but no conclusive evidence has yet been found that it did so. The stagnant

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and foul bottom waters, however, became stirred and purified by stronger currents than had existed in Cleveland time, and these currents locally stirred up the black mud and relaid it as the initial deposit of the Bedford. With the sweetening of the waters a bottom fauna entered the basin and lived most abundantly where the bottom mud was least stirred by currents. But the organisms were mostly small forms with thin shells that were badly broken up by the moving water. Soon the rate of the coming of mud into the basin increased, and locally stronger currents swept in and deposited great lenses of fine sand. The muddied waters disagreed with the fauna, which dwindled and vanished rather early, so that the waters of the basin during the greater part of Bedford time held but little life. The waters probably entered from the south, and the basin was landlocked on the west, north, and east sides. Neither the formation nor its fauna are known in western Pennsylvania. Rapid deposition seems to have quickly shallowed the basin, and the upper part of the Bedford, particularly the red Bedford, suggests deposition on shallow mud flats during climatic aridity.

CARBONIFEROUS PERIOD

MISSISSIPPIAN EPOCH

Berea sedimentation. At the end of the Bedford epoch an uplift of the lands on the north and west carried the Cleveland district above sea level and converted it into a low plain but with a surface gradient sufficiently steep and with bordering lands sufficiently high to enable the streams to bring down quantities of sand. The transporting currents channeled away the underlying muds of the Bedford and filled the excavations with sand, the channels being deepest where the land was highest—that is, at the northwest. The sands were spread broadly over the low plain that formed the general delta region. Abundant fragments of land plants were brought down by occasional floods and buried in the sands, and lumps of wet clay were also transported and deposited. Floods also brought down schools of freshwater fishes, some of which became stranded in pools on the delta surface as the flood waters fell, were killed by the drying up of the pools, and were covered by the sands of another flood and preserved as fossils. The numerous specimens of the fossil fish Gonatodus brainerdi found on the surface of a single layer in a single locality at Chagrin Falls are to be accounted for by some such process.

While the delta formation was being laid down in the Cleveland district the southeast slope of the land caused the deposits to be made beneath sea level in that direction, and this delta formation thus grades laterally into a finer-grained sandstone that carries marine

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fossils, as the Berea does in western Pennsylvania and in southern Ohio. During Berea time slow subsidence was in progress, and the sea came nearer and nearer to the Cleveland district, so that in the final stages of the deposition the delta surface was approximately at sea level, and storm waves could occasionally sweep in over this surface and bring a few worn marine shells to be deposited upon and be covered by the sand.

In contrast with that of the Bedford the Berea climate seems to have been moist and cool, as suggested by the abundant plant fragments and their carbonized condition and by the clay lumps found in the sands.

Orangeville sedimentation.—Continued depression, which lowered the adjacent lands, brought about a cessation of the sand supply and terminated Berea deposition. A renewal of marine conditions in northern Ohio followed. The waters slightly reworked the surface material of the Berea and produced from it a thin sandy stratum that subsequently became cemented by pyrite and forms the peculiar black layer of sand that is everywhere the Orangeville base. There was a break in sedimentation as one set of conditions passed into the other, but only for a short time. Then mud began to be washed into the subsiding basin, but the process was soon interrupted for a brief time by the incursion of sand that forms the thin Aurora sandstone near the base of the formation. The deposition of mud was. quickly resumed and continued with little variation until the full thickness of the formation had been deposited. The conditions were those of black shale formation, including quiet water and foul bottom from decaying organic matter. Bottom life was scarce, but. swimming forms, including large sharks, thrived, especially early in the epoch.

Sharpsville and Meadrille submergence.—The black shales of the Orangeville are followed by the sandy beds of the Sharpsville. The change in sedimentation indicates oscillation and increased altitude in the bordering lands. The sharpness of the break suggests a pause in sedimentation, though there is no evidence of uplift, and the interval seems to have been very brief. The Sharpsville currents cleared out the foul waters of the Orangeville basin, and a fairly abundant. fauna came in. Fragments of land plants are common, showing that the northern shore of the Sharpsville basin was not far away. The basin gradually deepened, and the sand was followed by the mud of the Meadville shale, with occasional incursions of sand that became more frequent in the later stages of Meadville time. Conditions. were more favorable for an abundant marine fauna than any that had prevailed in the district since Onondaga and Hamilton time, and they became steadily more favorable as Meadville time went on. Yet barren beds alternate with the fossiliferous beds, hence it is

evident that conditions varied and the fauna increased or diminished as they changed.

Nothing positive can be said concerning the climatic conditions that prevailed in the district during Orangeville and Meadville time. In discussing beds of about the same age in Michigan, Lane 10 states that "the abundance of mica and sand indicates rapid land waste and rock decay, while the abundant bits of vegetation show that there was abundant plant life. Both facts point to a relatively humid climate." These conclusions seem probable and applicable to the Meadville, whose climate was very likely moist and cool, though less markedly so than that of the Berea. It was tending toward the arid condition that followed.

Later Mississippian time.-In the Cleveland district no record remains of any deposits that may have been formed between the end of the Meadville and the beginning of Sharon deposition. The Black Hand and Logan formations of central Ohio lie above the Meadville, and their character indicates increased slopes in bordering lands, so that the streams carried coarser, often much coarser material. As these formations are present 25 miles to the south, it is possible that they were deposited over the Cleveland district and then worn away before the Sharon was laid down. It is also possible that the sea was withdrawn from the district at the end of the Meadville epoch and so remained during Black Hand and Logan time. The former alternative requires more erosion than the latter to produce the surface upon which the Sharon was deposited and allows less time in which to do it. The sea was certainly withdrawn at least as early as the end of the Logan epoch, the entire district becoming land.

A later Mississippian submergence, which was most prolonged in the region of the Mississippi Valley, involved southern and central Ohio for a time, and a thin deposit of calcareous mud, now the Maxville limestone, was laid down in a clear, shallow sea, but there is no evidence that this invasion reached as far north in Ohio as the Cleveland district. During this later part of the Mississippian epoch the climate became arid, and there was a salt lake in the Lower Peninsula of Michigan, where gypsum and rock salt were deposited during part of the time. At the end of the Mississippian epoch the sea was withdrawn over a wide area. The Cleveland district had become gently warped along an axis of elevation that coincides with the Chagrin Valley, and the warped beds were deeply truncated by erosion during this interval. The entire thickness of the Meadville shale was worn away along the axis of the warp, and much of its thickness elsewhere. If the Black Hand and Logan were deposited in the Cleveland district they were completely eroded away at this time.

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19 Lane, A, C., Michigan Geol. Survey, vol. 7, pt. 2, p. 23, 1900.

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