404 THE POPULAR SCIENCE MONTHLY. 



sion by the approval of his work which was given by the venera- 

 ble Prof. W. B. Rogers, then at the head of the Massachusetts 

 Institute of Technology, and for so long a time connected with 

 the Geological Survey of Pennsylvania and the adjoining Appa- 

 lachian region. 



" During all his earnest search for the truths of Nature, Lewis 

 was stimulated by the thought that man does not live by bread 

 alone, but that he who ministers to the mental wants of the race 

 by discovering truth and bringing it within reach of the general 

 apprehension is as truly a philanthropist as he who ministers to 

 their bodily comfort. In all these aims it is gratifying to know 

 that his wife most heartily coincided. A great truth of Nature, 

 like the wonderful history of the Glacial period, when it finds its 

 way into the school-books of the children and into works of gen- 

 eral literature, is of incalculable utility in the intellectual devel- 

 opment of mankind." 



"Prof. Lewis first became specially interested," writes Mr. 

 Upham, " in the glacial drift and its terminal moraine during the 

 latter part of the year 1880, when, in company with Prof. G. F. 

 Wright, he studied the remarkable osars of Andover, Mass., the 

 gravel of Trenton, N. J., containing palaeolithic implements, the 

 drift deposits of the vicinity of New Haven, Conn., under the 

 guidance of Prof. Dana, and finally the terminal moraine in east- 

 ern Pennsylvania between the Delaware and Lehigh Rivers. The 

 following year Profs. Lewis and Wright traversed together the 

 southern border of the drift through Pennsylvania from Belvi- 

 dere, on the Delaware, west-northwesterly more than two hundred 

 miles across the ridges of the Alleghanies, to Little Valley, near 

 Salamanca, N. Y., and thence southwesterly one hundred and 

 thirty miles to the line dividing Pennsylvania and Ohio, which it 

 crosses about fifteen miles north of the Ohio River. The report 

 of this survey of the terminal moraine was published in 1884, 

 forming Volume Z of the reports of progress of the Second Geo- 

 logical Survey of Pennsylvania. 



" With the similar exploration of other portions of this great 

 moraine done a few years earlier by Prof. Chamberlin in Wiscon- 

 sin, Profs. Cook and Smock in New Jersey, and Mr. Warren 

 Upham in Long Island, thence eastward to Nantucket and Cape 

 Cod, and also in Minnesota, it completed the demonstration 

 of the formation of the North American drift by the agency of 

 land-ice. 



" The observations of the moraine in Pennsylvania, detailed in 

 this volume, are summarized by Prof. Lewis as follows : ' The 

 line separating the glaciated from the non-glaciated regions is 

 defined by a remarkable accumulation of unstratified drift ma- 

 terial and bowlders, which, heaped up into irregular hills and 



