18 PROCEEDINGS OF THE AMHERST MEETING 



the Popular Science Monthly for June, 1894. The area of Lake Ohio 

 had been estimated as about 20,000 square miles, its depth at Pittsburgh 

 having been not less than 300 feet. It belonged to the culmination of 

 the Illinoisan stage or epoch of the Glacial period, when this part of the 

 ice-sheet east of the Mississippi attained its greatest thickness and exten- 

 sion. The duration of the Cincinnati glacial dam and lake, as for the 

 far larger glacial lake Agassiz, was very probably no longer than a few 

 thousand years; or perhaps only a few centuries of exceptional snowfall 

 witnessed the maximum accumulation and advance of the edge of the 

 great ice-field, doubtless fluctuating in its height and boundary, which 

 obstructed the Ohio Eiver. 



Professor Wright was commissioned in 1881 by the United States 

 Geological Survey to complete the examination and mapping of the lim- 

 its of the drift in southern Illinois to the Mississippi Eiver, with revision 

 of previous work eastward, which led to his publication in 1890 of Bulle- 

 tin Number 58, "The Glacial Boundary in Western Pennsylvania, Ohio, 

 Kentucky, Indiana, and Illinois." The glacial lake Ohio is quite ably 

 discussed and defended by this report, with consideration of an intro- 

 duction by Professor Chamberlin in attempted refutation, whereby he 

 claimed that the valley drift terraces fail to record the lake's existence, 

 as it had been affirmed by Wright, I. C. White, J. P. Lesley, and others. 



In 1886 Wright spent the month of August, with his classmate, Eev. 

 J. L. Patton, and S. Prentiss Baldwin, in making a survey of the Muir 

 glacier, at the head of Glacier Bay, in Alaska. From comparison of 

 their observations with those of others, he wrote in 1916 as follows, 

 noting great changes of this glacier : 



"Our measurements established a rate of motion in the center of the glacier 

 which exceeded anything found elsewhere outside of Greenland. Moreover, 

 we collected evidence that the front of the glacier had withdrawn more than 

 twenty miles in the hundred years which had elapsed since Vancouver visited 

 the region, in the latter part of the eighteenth century. My inferences on this 

 point were amply sustained by. Prof. H. F. Reid, who studied the glacier and 

 the region round about four years after my visit. Moreover, from surveys 

 made twenty-five years later, it appeared that the recession of the front has 

 continued at about the same rate which we had inferred for the previous 

 century. In 1909 the front was seven miles and a half farther back than it 

 was in 1886, when my photographs were made, while the surface had been 

 lowered, by melting, 700 feet. These facts, as they become known and appreci- 

 ated, cannot help having great influence in modifying current theories about 

 the time which has elapsed since the ice retired from the glaciated area in 

 the United States and Canada." 



On his return from the Muir glacier, Wright was invited to give a 

 course of eight lectures before the Lowell Institute in Boston, which, 



