HE YOSEMITE. 263 



report 1 the writer gave a 

 general account of stream corrasion. Necessarily in 

 such a report the subject could not be dealt with in 

 detail. In the present note a more detailed account 

 is given of the cirque, and the "steps" and "treads" of 

 Alpine Valleys so as to make the statement of stream 

 mechanics as simple as possible. Prom the principles here 

 discussed the general case of valley overdeepening by ice 

 may be easily understood. A special application of these 

 principles is made to the case of both the Yosemite and 

 the associated valleys in California. The scope of the 

 following note is as follows: — 



1. In the chapter on the psychological aspect of the 

 problem, the main reasons are given for the great diver- 

 gence of opinion on a problem which should have been easily 

 amenable to proof. [Incideutly it shows how difficult it 

 must be to arrive at trustworthy conclusions concerning 

 the origin of the earth, the condition of its central portions 

 or even the origin of the Archaean Complex when the most 

 acute geological intellects are unable to agree as to the 

 activities involved in the production in recent geographical 

 time of a mere surface form such as a typical Alpine cirque 

 or lake basin.] The writer feels that the psychological 

 factor has entered so largely into the question of glacial 

 corrasion, that a clear statement of such factor is necessary, 

 otherwise the young geologist may become hopelessly 

 involved in dynamical difficulties. Such a student must 

 take heed to free himself from the adverse suggestions 

 received possibly in the lecture room, and ho must test the 

 soundness of his academic training by submitting the teach- 

 ing there received to the rigorous test of field and laboratory 

 observation. He must remember that one good observation 

 leads nearer to truth than a whole lifetime of reasoning 



1909, p. 204. 3 ' ' " 0rnKOn 7 Tni% ' 5 * re<imS ' 



