ture of the regions within which the new fields are embraced, and the tracing of the chief factors that influence or control the productiveness of the oil rock, with the description of the special features and boundaries of the several fields and the setting forth of the leading facts and present development of these lately found sources of power. Two principal conditions under which the new oil rock had proved petroliferous on a large scale were found to be porosity, connected with and apparently dependent on the chemical transformation of the upper portion of the limestone, for a number of feet in thickness, into a highly crystalline dolomite; and a relief resulting from slight warping of the strata, whereby the common contents of the porous portions of the Trenton limestone had been differentiated by gravity, the gas and oil seeking the highest levels, and the salt water maintaining a lower but definite elevation in every field. Professor Orton found nothing in the new experience to make it safe to count the Trenton limestone an oil rock or a gas rock in any locality, unless it could be shown to have undergone the dolomitic replacement by which its porosity was assured; and even in case it had suffered this transformation it would not be found a reservoir of gas or oil in an important sense unless some parts of it had acquired the relief essential to the due separation of its liquid and gaseous contents.
The report on the Rock Waters of Ohio concerns, first, those waters, chiefly in the northwestern and western part of the State, that are obtained from a considerable depth as compared with ordinary wells, the knowledge of which was almost wholly derived from wells drilled in the search for oil and gas, and was necessarily fragmentary and incomplete; because water was not included among the objects of search, but was considered a hindrance and obstruction to be got out of the way as well as possible; and, second, flowing wells, including only those having considerable head of pressure and those occurring in considerable areas, all of which belong entirely to the drift. Further, a brief review is given of some facts of unusual interest that were developed in the deep drillings concerning the preglacial drainage system of the part of the State in question. Indications of old river channels, one of which seems to have been extensive, were found at several points. Among the curious results of these studies was the conclusion, "seeming to be already established," "that the Ohio River, as we now know the stream, is of recent origin, and that the main volume of water gathered in it at the present time originally flowed across the State to the northward at least as far as Auglaize and Mercer Counties, where it turned to the westward toward the present lines of Wabash drainage in Indiana." Professor Orton seems to have
