34 GLACIAL AND SURFACE GEOLOGY OF THE PACIFIC COAST. 



been obtained in this connection during the various explorations and recon- 

 naissances of the Geological Survey in that region. 



At the time of the beginning of the California Survey nothing was known 

 in regard to glacial phenomena in the Far West. It was generally assumed 

 that the ice-capping of the northern hemisphere was something which ex- 

 tended all around the pole, and it was presumed that what was true for New 

 England in respect to ice-action would be found to hold also in similar lati- 

 tudes in the western regions on to the Pacific. 



It was with no small interest, therefore, that we began to study, in 1860, 

 the distribution of the surface detritus on the Pacific coast with reference to 

 the question of ice-action. Our first year's work was entirelj' or chiefly in the 

 Coast Eanges, and it was clearly established by our examinations, which 

 during that year extended from near the southern border of California to a 

 hundred miles north of the Bay of San Francisco, that here Avas no question 

 of either glacial or northern drift. All the loose materials on tlie surllice 

 showed themselves to have been distributed by causes similar to those now 

 in action. Detrital materials were always found to have been carried by 

 water down the slopes of the mountain ranges. The source of the debris at 

 the mouth of any canon was always to be found up the canon, and not at any 

 point to the north or in any other general direction. There was no striation, 

 or other marking of the rock surfaces, such as could only be attributed to 

 the sliding over them of icy masses. The next year, however, took us into 

 the Sierra Nevada, and here we did not fliil to discover abundant proof of 

 the former existence of glaciei's on a large scale. The exploration of 

 1862, 1863, and 1864 showed us that large glaciers had once covered a con- 

 siderable portion of the Sierra, but only the higher portion ; that in certain 

 favorable positions, where there was a large gathering-ground tor the ice, — 

 a cirque of vast dimensions, as at the head of the Tuolumne River, — these 

 glaciers had tbrmerly descended to a level of between 3,000 and 4,000 feet 

 above the sea. In the Southern High Sierra, between the parallels of 36^ 

 and 37^ 30', the same condition of things was observed in 1864; abundant 

 proof was obtained of the former existence of glaciers, v/hich had, under 

 favorable circumstances, descended to a pretty low level, and had left, as 

 proof of their former presence, magnificent moraines, — medial, lateral, and 

 terminal. The rapid rise of the Sierra as we proceed southwards from the 

 head of the Tuolumne, fully compensates for the decreased latitude, so that 

 the glaciers were as fully developed between the parallels of 36^ 30' and 



