272 PROCEEDINGS OF THE CALIFORNIA 



however, that there is no true Northern Drift within the limits of this State. 

 Our detrital materials, which often form deposits of great extent and thickness, 

 are invariably found to have been dependent for their origin and present posi- 

 tion on causes similar to those now in action, and to have been deposited on 

 the flanks and ut the bases of the nearest mountain ranges by currents of water 

 rushing down their slopes. While we have abundant evidence of the former 

 existence of extensive glaciers in the Sierra Nevada, there is no reason to sup- 

 pose that this ice was to any extent an effective agent in the transportation of 

 the superficial detritus now resting on the flanks of the mountains. The glaciers 

 were confined to the most elevated portions of the mountains, and although the 

 moraines which they have left as evidences of their former extension are often 

 large and conspicuous, they are insignificant in comparison with the detrital 

 masses formed by aqueous erosion. There is nothing anywhere in California 

 which indicates a general glacial epoch during which ice covered the whole 

 country and moved bodies of detritus over the surface, independently of its 

 present configuration, as is seen throughout the Northeastern States. 



The same condition of things prevails in Nevada and through Oregon, as 

 far as explored by the members of the Survey. The detritus seems alway to 

 be accumulated at the base of the mountains — gravel, holders, and sand lying 

 below and not far distant from the beds of rock of which these materials once 

 formed a part, and from which they appear to have been detached by weather- 

 ing and aqueous erosion. 



From the observations of Messrs. Ashburner and Dall, it would appear that 

 no evidences of Northern Drift have yet been detected on this Coast, even as 

 far north as British Columbia or Russian America. Neither of these gentle- 

 men has observed any indication of a transportation of drift materials from the 

 north towards the south, or of any condition of things similar to that which 

 must have existed in the Eastern States during the diluvial epoch. 



On examining the published records of explorers in the central portion of the 

 Continent, it will be noticed that there is strong reason to believe that the 

 absence of the Northern drift formation is not peculiar to the States along the 

 Pacific Coast ; but that the whole region west of the Rocky Mountains is also 

 destitute of any indications of a detrital formation moved over the surface in one 

 direction by any great general cause. Judging from our present stock of evi- 

 dence, I am inclined to draw the line which limits the Northern Drift formation 

 on the south and west approximately from the mouth of the Ohio to the head- 

 waters of the Saskatchewan River. 



It is evident that these facts should be taken into account in theorizing on 

 the origin and cause of the drift. If, as stated above, the transporting agent 

 has been limited in its field of action to the eastern and northeastern portion of 

 our Continent, the phenomenon is seen at once to have become, in a measure, a 

 local one — at least much more local than has hitherto been usually assumed by 

 those geologists who have adopted the glacier theory of the drift. 



Professor Whitney remarked that he was particularly desirous 

 of introducing the subject on this occasion, in order that he might 



