Page:The Journal of geology (IA journalofgeology11893univ).pdf/143

In Ohio, as in other portions of the Mississippi basin, clear and unmistakable evidence of discontinuity in the drift deposition has long been recognized. Whittlesey, Newberry and Orton were among the first to announce the occurrence of buried soils in the North American drift, and they each drew illustrations from Southwestern Ohio. A few years later Professor Chamberlin discovered evidences of late advances in which the outline of the ice-sheet was very different from that of the glacial boundary. He also observed that the aspect of the drift is much fresher than in the outlying earlier drift. He further noted the evidence of valley erosion of considerable amount effected in the interval between the formation of two moraines, or more accurately two sets of moraines, in Western Ohio, the oldest of which is much younger than the earliest drift sheet, as will be seen below. My own studies, carried on under the direction of Professor Chamberlin, have brought out more fully the nature and value of these and other intervals which exist in that region. No less than nine of the twelve criteria for discrimination between glacial epochs set forth by Professor Salisbury in the opening number of this Journal have been found, viz.: (1) Buried soils. (2) Buried fossiliferous silts. (3) Differential weathering. (4) Differential subaërial erosion. (5) Excavation of valleys between successive depositions of drift. (6) Changes in the course of ice-currents and in the outline of the ice margin. (7) Superposition of drift of different physical constitution. (8) Varying altitudes of the land. (9) Variations in vigor of ice action. Although the present state of knowledge of the Ohio drift is far from being as complete as one could desire, it seems profitable to review such evidence as throws light upon the value of the several intervals which mark the glacial succession in that state. In the western portion of