Page:The Journal of geology (IA journalofgeology11893univers).pdf/199

Tertiary and Quarternary Stream Erosion of North America, by Warren Upham; The Emergence of Springs, by T. C. Hopkins.

As the writer was unable to hear a considerable number of these papers his notes must be confined to comparatively few of them. The paper of Mr. Lincoln presented a very interesting sketch of the quite remarkable evidences of glacial erosion and modification of surface in the Finger Lake region of New York. He showed, successfully we think, that the existing topography could not have arisen in its present form through the agency of subaërial degradation alone nor by the simple deposit of drift material on a surface so produced, but that a very notable amount of reshaping of the rock-surface was the result of glacial abrasion.

Mr. Frank Leverett made a quite important contribution to the data bearing upon the stages and duration of the earlier glacial epoch. He has recently discovered evidence that the Rock River formerly flowed nearly due south from a point near Rockford into the Green River basin, and presumably onward to the great bend of the Illinois River, near Hennepin, where an old deep channel exists. From this course the river was diverted to its present south-westerly course by the earliest or at least one of the earlier stages of the ice invasion of that region. Between the time of this diversion and the stage at which the kettle moraine was formed across the Rock River about forty miles to the north, near Janesville, Wis., the river cut a trench in rock across a succession of preglacial cols to maximum depths estimated at 100 to 125 feet. Mr. Leverett made careful estimates of the total amount of rock excavation and found it to amount to one square mile 1100 feet deep. Stated in another form, this equals a trench 100 feet deep, one mile wide and eleven miles long, or one-half mile wide and twenty-two miles long. After the trench had been cut, the glacial wash from the outer edge of the kettle moraine partially filled the trench as shown by remnants of terraces still existing at different points along it. The amount of this filling within the area of the above computation is estimated as one square mile 900 feet thick or ⁠9/11⁠ of the amount of rock excavation. Since the formation of these gravels the