Xewberry.] ••'^ [Nov. 4, 



pression on topograph}' except by the accumulation of morainic material, and 

 also that ice has had no agency in the excavating of the lake basins, are 

 alike disproved by my own observations. Any one who has visited the 

 present termini of the Alpine glaciers cannot fail to have remarked the 

 roc7ies moutonnees and the broadly excavated troughs, the work of the 

 glaciers when they had greater reach. He will also have noticed that 

 these glacial troughs, under and beyond the present glaciers, are furrowed 

 by deep and narrow channels, the work of the streams flowing from the 

 melting ice. Here we obtain conclusive evidence that ice has erosive 

 power, and have, on a small scale, typical examples of the kinds of erosion 

 wrought by ice and water. The higher portions of the Sierra Nevada, and 

 the whole summit of the Cascade mountains bear such indisputable evidence 

 of the erosive action of ice that it is incomprehensible that any one should 

 have seen this record and deny its validity. On the Cascade mountains there 

 are thousands of square miles over which the rocks are planed down, 

 grooved and furrowed, where the rough and ragged summits are reduced 

 to roches moutonnees and enough material has been removed by ice 

 to till all the water-cut channels of the continent. In the Report of the 

 Geological Survey of Ohio I have described in detail the evidence of the 

 action of ice in forming the basin of Lake Erie. No one can visit the 

 group of islands off Sandusky without being convinced that they are 

 carved by ice out of the solid rock. Their sides and surfaces are every- 

 where glaciated, and areas of acres in extent planed doAvn to the smooth- 

 ness of a house floor. The corals and other fossils which fill the limestone 

 are here cut across as smoothly as it could be done by hand ; and as I have 

 elsewhere shown, the direction of the furrows and the trails left behind 

 chert masses in the limestone, prove that the ice moved in the line of the 

 major axis of Lake Erie, and from the north-east toward the south-west. 

 Similar facts both in regard to rock striation and the transport of mateiial 

 have been observed about Lake Ontario, Lake Huron, Lake Michigan and 

 Lake Superior. 



The manner in which ice accomplishes the erosion effected b}'- it, is no 

 mystery, as any one who has seen a glacier has seen the agent in action . 

 The soft ice simply becomes a great emery wheel. Rocks, gravel and sand 

 are frozen into its under surface or are spread beneath it and pressed down 

 upon its bed with the enormous weight of the moving mass ; the result is 

 a grinding that nothing can resist. The ground up material is "till '' or 

 boulder clay, sand, gravel and boulders, and this residue, perhaps insig- 

 nificant in quantity compared with the amount produced, covers literally 

 hundreds of thousands of square miles on this continent alone. How, in 

 the face of these facts, can any one say, ice has no erosive power? Prof. 

 Spencer misunderstands and misrepresents me when he imputes to "me any 

 vacillation of opinion or any uncertainty in regard to the agencies which 

 have excavated the lake basins. From the first I have recognized the 

 existence of an ancient river draining the lake basins at a low level, and 

 was by many years the first to indicate the existence of such a stream, but 



