338 



NATURE 



[Feb. 15, 1877 



pages without a conviction that he correctly regards the 

 whole erosion of the Colorado region as one vast con- 



tinuous process in which air, rain, frosts, and rivers have 

 been the main agents. 



Fig. I. — The Needles, looking South-westerly. 



i 



I 



Fig. 2.— Lower San Juan, looking West. 



The observations contained in this Report upon the I the horizontality of the stratified formations of the great 

 ti ucture of the isolated ridges which now and then disturb j plain are of considerable interest and importance. They 



II 



