1885.] NATURAL SCIENCES OP PHILADELPHIA. 171 



On the high mountain plateau of Potter County, Pa., for 

 example, at an elevation of 2500 feet, although the Allegheny 

 River flowed at the very foot of the glacier, there is no drift in 

 the valley of the river, and no indication of any drainage to the 

 south ; while north of the moraine the whole country is covered 

 with clays, terrace plains, kames and ever}' indication of the 

 presence of both ice and water. 



Again, in Columbia County, Pa., although Fishing Creek flows 

 in front of the edge of the ice sheet which once rested on its 

 eastern bank, there are no gravel deposits in the creek ; while 

 immediately back of the moraine we find them in great quantities, 

 leading around to another outlet. 



So on the Pocono plateau, in Carbon Co., the drainage was 

 reversed ; while in Northampton County, and Monroe County it 

 was clearly in both directions, outward and inward. 



The writer has adduced evidence that the Allegheny River, 

 near Olean, N. Y., flowed into the glacier and out of it again in 

 the same channel that it now occupies ; flowing in a subglacial 

 channel through or under a tongue of ice ten miles broad by two 

 miles long. 1 



Everj^where there are indications of a great subglacial drainage. 

 The observations of other geologists, especially of Prof. New- 

 berry, in Ohio, lead to the same conclusion. Studies among 

 modern glaciers confirm these interpretations of glacial phe- 

 nomena. 



Prof. Nordenskiold described the " large and swift rivers," 

 plunging from the surface into profound crevasses of the Green- 

 land ice-sheet, and Dr. Rink speaks of the copious subglacial 

 streams which flow out from under the Greenland ice. 



From beneath the Muir glacier of Alaska, 2 there issues a sub- 

 glacial stream 100 feet wide, and 4 feet in average depth, the flow 

 being the same winter and summer. Prof. Dana 3 has rightly 

 assumed that the ice sheet of North America would have had 

 " subglacial streams as much more extensive than those of Green- 

 land, as the precipitation was more copious and the drainage 

 areas larger." 



Much of the boulder clay and till throughout the lower por- 



1 Report Z, p. 154. 



2 Meehan, Proc. Acad. Nat. Sc. Phila., 1883, p. 249. 



3 Am. Jour. Sc, xxii, p. 366, 1882. 



