274 THE ICE AGE IN~ NORTH AMERICA. 



ancient glaciers, and were also the last strongholds to be aban« 

 doned when the reign of ice approached an end. 



Such amphitheatres are known in all mountain-regions 

 where glaciers haye existed. It has been the good fortune of 

 the writer to examine them on some of the higher peaks of 

 Colorado and New Mexico, about the crests of the Wahsatch 

 and East Humboldt Mountains, as well as in Switzerland and 

 New Zealand. Their origin is somewhat problematic, and has 

 occasioned much discussion, as is well known to all who have 

 followed the growth of glacial literature. 



In an article on the formation of cirques, by T. G-. Bon- 

 ney,* an attempt was made to prove that these peculiar feat- 

 ures of mountain sculpture are the result of stream-erosion, and 

 owe few if any of their characteristics to ice-action. 



The studies of B. Gastaldi,f on the effects of glacial ero- 

 sion in Alpine valleys, led him to reject Bonney's hypothesis, 

 and to conclude that they are a result of ice-erosion. 



The most extended as well as the most instructive essay 

 concerning their formation that has come under the writer's 

 notice is from the pen of Amund Helland, entitled "On the 

 Ice-Fiords of North Greenland, and on the Formation of 

 Fiords, Lakes, and Cirques in Norway and Greenland." J In 

 this essay a clear and concise description of the cirques of 

 Norway, Switzerland, and other regions is given, together 

 with a brief summary of the various hypotheses that have 

 been advanced in explanation of their origin. Strong evi- 

 dence is also presented to show that they are a result of glacial 

 action. In Helland's essay are included the views of Lorange, 

 of the Norwegian Royal Engineers, who arrived at the con- 

 clusion that they are formed principally by the effects of 

 great changes of temperature in the vicinity of glaciers. We 

 quote Lorange's observations and conclusions as stated by Hel- 

 land : 



"Under the glaciers in cirques, where a space intervened 

 between the bed of the cirque and the ice, he saw a great many 



* "Quarterly Journal of the Geological Society," London, vol. xxviii, 1872, 

 pp. 312-324. 



f Ibid., vol. xxix, 1872, pp. 396-401. 

 X Ibid., vol. xxxiii, 1873, pp. 142-176. 



