72 GLACIAL AND SURFACE GEOLOGY OF THE PACIFIC COAST. 



of drift ill these mountains. The descriptions of the surface convey the idea 

 most clearly that all the detrital material is of local origin, and that no part 

 of the surface has ever been covered with ice. 



In the preceding pages all that appears to be definitely known in regard 

 to the former glaciation of the surface within the borders of California, and 

 ill the Cordilleras south of the United States boundary line, has been jila-ced 

 before the reader; if not with full details, at least with sufficient minuteness 

 to afford a satisfactory basis for a discussion of the phenomena in their con- 

 nection with other evidences of climatic change. 



It will be readily seen that the facts are all of a simple character and 

 entirely in harmony not only with each other, but with the present topo- 

 graphical features of the region included within the field of observation. 

 Briefly resumed, these facts are as follows : In California, the Great Basin, 

 and the Rocky Mountains, up to the head of the Missouri River, the highest 

 portions of the most elevated ranges were formerly covered with glaciers, 

 some of which were very extensive, reaching a development of forty miles, 

 or even more, in length, and of five or six in breadth, — in short, equal- 

 ling or even surpassing the largest Alpine ice-fields of the present day. 

 These glaciers nowhere descended to within several thousand feet of the sea- 

 level. They show a tendency to descend lower as we proceed northward ; 

 but this tendency is, to a considerable degree, nullified by the diminished 

 altitude of the ranges, the highest portion of the Cordilleras lying, in Cali- 

 fornia, between the parallels of 36° and 39°, and widening as it crosses the 

 country, so that its northern limit in the Rocky Mountains is a little beyond 

 the parallel of 44°. No proofs whatever of former glaciation have been de- 

 tected by competent observers to the south of latitude 36°. All through the 

 region indicated the detrital materials have been carried from the higlier 

 toward the lower areas, in strict harmony with the present configuration of 

 the country. A large part of this carrying has been done by water unaided 

 by ice, for the formerly glaciated area occupies but a very small portion of 

 the surface. Where glaciers have existed, there all the signs of their former 

 presence, such as moraines, striated and polished surfaces, and rounded ledges, 

 can be recognized without the slightest difficulty, so that, with accurate 

 maps and careful observations by competent persons, the area forme ily cov- 

 ered by ice could, and probabl_y will at some future time, be laid down with 

 the closest approach to accurac}-. And, of course, from wliiit has been said 

 above, it will be readily perceived that there is no such thing as " Northern 



