14 LAKES OF NORTH AMERICA. 



as the evidence from which it is concluded that many smoothed and stri- 

 ated rock surfaces are due to the same agency. The rock basins of the 

 character here referred to, are confined to regions of former glaciation, not 

 only in America but on other continents, and are wanting where other 

 evidences of ice action are absent. The interiors of the basins themselves 

 are smoothed and striated, and bear incontestable evidence that in part at 

 least, they are due to the abrasion of sand-charged ice. These more 

 general considerations are in such harmony with wdiat is known of the 

 work of ice streams, that they carry even more weight than special 

 studies of individual lakes. 



Although the evidence leading to the conclusion that many rock 

 basins in glaciated regions are essentially of glacial origin, seems to the 

 writer to be conclusive, it is but just to state that, even after thirty years . 

 of ardent controversy, there is still a difference in opinion among geolo- 

 gists and others, in reference to the abrading power of moving ice, and its 

 ability to erode rock basins. The literature bearing on this question is so 

 voluminous that it is impracticable to present even an abstract of it at the 

 present time.^ 



Without considering further the results of the destructive action of 

 glaciers, let us see what is the character of the basin they produce by 

 construction. Fortunately in this connection there is little difference of 

 opinion. 



The terminal moraines left by Alpine glaciers in their retreat, fre- 

 quently form crescent-shaped piles of debris, convex down stream, wliich 

 act as dams, and retain lakes. Hundreds and probably thousands of 

 examples of lakes held in check by obstructions of this character, exist in 

 the valleys of the Cordilleras, and are common in every formerly glaciated 

 mountainous reofion. The Twin lakes in the Arkansas vallev, Colorado,^ 

 several small lakes on the Avest side of Mono valley, California,'^ and 

 numerous sheets of clear water in the Wasatch mountains, Utah, so well 

 known to tourists, are types of this class. Similar lakes occur about the 



1 This subject has received special attention since the appearance of a celebrated paper 

 by Ramsay, "On the glacial origin of certain Swiss lakes," Quar. Jour. Geol. Soc, vol. 18, 

 p. 185 ; but a unanimous conclusion has not been reached, as may be seen by consulting 

 Nature for 1893-94. The present status of this interesting controversy is presented in a 

 paper by T. G. Bonney, and accompanying discussions, in the Geographical Journal of the 

 Royal Geographical Society, vol. 1, 1893, pp. 481-504. 



2 F. V. Hayden, U. S. Geol. and Geog. Surv. of the Territories, Ann. Rep., 1874, pp. 

 47-53. J. J. Stevenson, Explorations and Surveys vrest of the 100th Meridian (" Wheeler 

 Survey" ), vol. 3, 1875, pp. 441-444. 



3 I. C. Russell, U. S. Geo!. Surv., 8th Ann. Rep., 1880-87, PI. 35. 



