24 GLACIAL AND SURFACE GEOLOGY OF THE PACIFIC COAST. 



ioning the grand peaks and domes of the Sierra. There are few parts of 

 the world where the dynamical agencies of ice in past times can be more 

 conveniently and profitably studied than in the region in question; but it is 

 very desirable that such study should not be entered upon with precon- 

 ceived theories, and that it should have been either preceded or at least 

 afterwards supplemented by analogous studies in other regions of present 

 extensive glaciation, like Switzerland or Norway. Such study on the part 

 of some of those who have given their opinions with the greatest fluency 

 in reference to supposed glacier work on the Pacific coast would perhaps 

 have made these writers a little more cautious in advancing their crude and 

 often utterly absurd theories. 



The reason of the very plain and obvious nature of the former glacier 

 work in the SieiTa is due in large part to the very recent date of its occur- 

 rence ; and this fact links itself unmistakably with another important one, 

 namely, that the glaciation of the range is Jibsolutely and entirely in har- 

 mony with its present topography. The whole body of fiicts collected hy 

 the Geological Survey shows most clearly that there has been no essential 

 change in altitude of the formerly glaciated regions since the ice disap- 

 peared ; and, still further, that all the features of the surface — valley, gorge, 

 caiion, cliff, dome, ridge — remain just as they were when the climatic con- 

 ditions changed so as to bring about the shrinkage and final obliteration of 

 the once extensive ice-masses. It is even clear that the volcanic fires of the 

 Sierra were entirely spent before the glaciation of the range took place. In 

 short, the ice-pei'iod in California was the most recent of all the geological 

 phenomena there exhibited ; and, as will be clearly shown, it cannot be con- 

 sidered to have been removed by any but a very moderate amount of time 

 from the actual present. 



In commencing a rapid review of the former distribution of glaciers on the 

 Sierra, we may begin by referring to the well-known fact, that the range 

 sinks in general elevation as we proceed northward from the culminating 

 region in lat. 36' 30'; southward from this the range also breaks ofT quite 

 abruptly. Glacial phenomena are therefore cut off altogether, to the south 

 of 36°, by the rapid decrease of the range in altitude, combined with constant 

 diminution in latitude. To the north the falling off in altitude is partly 

 compensated by the more northei'ly position, so that we have a belt along 

 the Sierra of from three to four degrees in width, where the phenomena of 

 ancient glaciation are chiefly displayed. 



