Wright.] 60 [December 20, 



" During the glacial period, while so large a portion of the eastern 

 and northern states was covered by a more or less continuous ice 

 sheet, there were totally different conditions throughout the system of 

 the Cordilleras. No northern ice-field stretched over that elevated re- 

 gion, and the only glaciers were local mountain streams descending from 

 high centres of dispersion. The. northern peaks of the Cascade and 

 Sierra Nevada Ranges still hold in their glacial valleys, the shrunken 

 relics of the old ice period. To the south, where the climate no. 

 longer permits great annual accumulations of snow, all the higher 

 mountain ranges are scored by profound canons, from 3,000 to 6,000 

 feet deep, whose forms were greatly modified, if not actually determ- 

 ined, by the system of extinct glaciers. Besides the ordinary topo- 

 graphy of the ciercs de neve and the well known striated and polished 

 rocks, (roches moutonne'es^) dotted with huge erratics, there is a sys- 

 tem of splendidly preserved lateral and terminal moraines ; the 

 former traced along the flanks of the canons wherever the angle of 

 slope is sufficiently gentle to permit the accumulation of debris, and 

 the latter stretched across the canons at intervals, marking levels 

 where glaciers temporarily rested in their general retrogression. The 

 result is that all the great canons of the Sierra Nevada have at in- 

 tervals, for the upper thirty or forty miles of their descent, numerous 

 piles of terminal debris, besides frequent long stretches of lateral 

 moraines which have distinct ridge-like summits, as evenly graded as 

 a railway embankment. 



" During several summers I spent a great deal of time in the exami- 

 nation of these moraines, as well as of the erratics left in the bottoms 

 of the glacial troughs. The valley erratics were of two kinds ; blocks 

 of rock which had been transported on the surface of the glacier and 

 which sunk to the solid bottom when the ice finally melted ; the others 

 are fragments which were embedded in the bottom of the glacier. 

 The surface erratics are never striated and are usually of angular 

 forms, such as may be observed to-day upon any Swiss glacier or 

 upon the ice streams of northern California, Oregon and Washington 

 Territory. The bottom debris, upon the contrary, is always sharply 

 planed off on one side and evenly striated. The striae often run in 

 two directions, as if the blocks had been shifted in the ice and re- 

 ceived a second set of groupings. The character of the blocks com- 

 posing the lateral and terminal moraines differs altogether from both 

 of these. Near the source of supply, high up on the flanks of the 

 neves, it consists altogether of angular or rudely rounded fragments ; 



