dip southeast, it is obvious that a warp that increases the steepness of dip of the former must correspondingly diminish that of the latter. In other words, where the surface rocks have their steepest southwesterly dips those below ground would have their flattest. Such an area of increased southwest dips of the Mississippian rocks occupies the eastern two-thirds of the Berea quadrangle, and there the underground limestones must have a corresponding diminution in their southeast dip, hence must lie flatter than usual. This is the region. of gas production, a region where the dip, whether measured along an east-west or a north-south line, is much less than the normal.

The soft shales of the district in many places exhibit minor disturbances, both folding and thrust faulting. These are all of small extent, some of them are old and some very recent, and they have arisen from different causes. The shales at the base of the Berea are very liable to be disturbed, especially in the vicinity of the large channels. They are variously tilted and in some places are faulted. These disturbances were effected by the currents that brought in the Berea sands, the underlying mud being shifted about and slumping along the channel sides. The recent disturbances are all very local and surficial and may be due to expansion brought about by weathering. Their cause is not definitely known.

GEOLOGIC HISTORY

Beyond the bare statements that the Cleveland district had a preCambrian history whose records are wholly buried beyond our reach; that it no doubt shared in the general uplift of the continent at the end of pre-Cambrian time and remained a land area for a long interval; that it became submerged beneath the shallow 'waters of an Upper Cambrian sea; and that this submergence was followed by others in Ordovician time, nothing can be said as to its early geologic history. The lower 1,170 feet of rock in the Lorain well is of Ordovician age, but just what Ordovician groups are represented there it is impossible to say. The well record shows that the district was submerged during much of the Ordovician period and that a large thickness of deposits was formed. Probably the Trenton, Utica, Eden, and Maysville are all represented by deposits, showing submergence of the region during those epochs.

PALEOZOIC ERA

By H. P. CUSHING

ORDOVICIAN PERIOD

The oldest of the underground formations that is recognizable with any degree of certainty is the red shale, which is probably referable to the Queenston shale, of Richmond age, a formation whose nearest surface outcrops are those along the Niagara River and in Ontario.

These red shales are unfossiliferous and seem to represent a near-shore phase of the Richmond, laid down in shallow water on a slowly subsiding bottom, under conditions very unfavorable to life. The typical Richmond rocks, which are widely exposed in the region around Cincinnati, where they are full of marine fossils, were deposited farther offshore.

At the end of the Ordovician period the Cincinnati arch was domed and elevated above sea level as part of a general withdrawal of the sea that then took place. This arch has since remained as a positive feature of the continent, continuing as a land area or a submerged shoal throughout the remainder of the Paleozoic era. That the Cleveland district was also brought above sea level at this time is not definitely known, though regarded by many geologists as highly probable. If it was, the land was low and was not greatly eroded.

SILURIAN PERIOD

Whether the Silurian should be considered to begin with the Richmond or with the succeeding formation is a question upon which geologists are not entirely in accord. The United States Geological Survey, following the general practice, includes the Richmond in the Ordovician.

Above the red Queenston (?) shale of this area come alternating sandstones, shales, and thin limestones which are called the Clinton formation and which include the so-called Clinton gas sand but are probably referable in whole or large part to the Albion sandstone, a formation that underlies the true Clinton formation of New York. It is not known whether true Clinton beds are present or not, nor whether the district was continuously submerged or emerged one or more times during the interval. If it was emergent, depression followed, and clear, open marine conditions prevailed, during which the considerable thickness of limestones of Niagara age was laid down. This subsidence was long continued and widespread, and the clear waters of the sea were thronged with numerous and varied forms of life.

After the Niagara epoch the sea largely withdrew, and the district was occupied by landlocked waters, presumably near or at sea level, surrounded by very low lands. The climate became arid and caused the conversion of the water bodies into one or more salt lakes in which mud and thin beds of limestone were deposited, then beds of gypsum, and, in local areas where there was great concentration of the saline waters, beds of rock salt. The series of deposits is repeated several times and suggests corresponding variations in concentration of the waters, possibly due to fluctuation in the amount of rainfall. Under such conditions the Salina beds, of early Cayugan age, were laid down. The Salina waters covered a large part of New York and

Pennsylvania and also northeastern Ohio. The characteristic deposits cease a few miles west of the Cleveland district. Whether the waters were there but deposited no salts, or whether western Ohio was above the water level of the time and received no deposits, as the writer thinks, is a matter upon which geologists disagree.

After the Salina epoch the climate became less arid and the submergence more extensive, and under these conditions the water limes and some gypsum beds of the Bass Islands dolomite were deposited. The gypsum beds show that the climate was still arid, but the waters never became as concentrated as during the Salina and were often fresh enough to support a fauna, which however, was not a normal marine fauna but one of a few types that were adapted to thrive in the unusually salty waters of the basin.

DEVONIAN PERIOD

Sylvania and Lucas submergence. The succeeding Sylvania sandstone testifies to a great change in physical conditions. The excellent sizing of the grains, together with their rounded shapes and etched surfaces, certainly indicates that the sand was blown by winds and suggests desert conditions on neighboring lands and the continuance of climatic aridity. Whether the sand was deposited in water or on dry land is not certainly known, but the great contrast between the sandstone and the limestone above and below demonstrates a great change in physical conditions and argues for emergence of the district during the Sylvania epoch.

Renewed depression brought on the deposition of the Lucas dolomite. This also suggests deposition in a partly inclosed basin during climatic aridity and mostly in shallow water. In the upper part of the formation beds of limestone carrying a marine fauna appear. The district came above sea level at the end of the Lucas epoch and existed as an area of low land for a long time.

Onondaga submergence.-The Onondaga sea of the Middle Devonian was the next marine water to overspread the district. The land had been thoroughly base-leveled during the emergent period just preceding, so that the shallow Onondaga seas spread rather widely. The lands that bordered it were low and incapable of supplying much land wash, so that the waters were clear and peopled with an abundant marine fauna and supported extensive local coral reefs. The reefs indicate warm waters and supply part of the evidence that the marine invasion came from the south.

Hamilton submergence.-The limestone of Onondaga age terminates rather abruptly and is directly followed by the blue to brown beds of the Delaware limestone. Conditions in surrounding territory must have changed, as the beds of Hamilton age contain more land wash than those of Onondaga age; hence, the bordering lands must have

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 Hamilton 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