Studies in the Sierra 



73 



very end of the glacial epoch, soil would evidently have been 

 laid down in one continuous bed all the way back to the sum- 

 mit, because under these conditions every portion o£ the sur- 

 face in succession would have been loaded with terminal mo- 

 raine-belts pressed one against the other like plow-ridges. Un- 

 der the conditions which prevailed toward the close of the great 

 winter, the separate glaciers as well as the ice-sheet shallowed, 

 became torpid, and died away simultaneously throughout all 

 this upper region; no terminal moraines are therefore to be met 

 until we reach those of the small residual glaciers which took 

 shelter in the loftiest and coolest shadows of the summit peaks. 



Fig. 2. 



Nor will this state of things be wondered at, when we consider 

 how slight is the difference in elevation, and consequently in 

 climate, between the upper and lower limits (A and B, Fig. 2) 

 of this bare alpine bench, as compared with that of the slope (C 

 A) beneath it, upon which the soil-belt lies. 



The effect of shadows in determining the formation, size, 

 and distribution of glacial soil-beds must not be overlooked. 

 When the seasons grew warm and the long crooked glaciers 

 were driven from the sun-beaten summit bench, thousands of 

 small residual glaciers, from half a mile to two or three miles 

 in length, lingered on through many a century in the shelter of 

 frosty shadows. Accordingly, we find the moraines of these 

 hiding glaciers in the highest and coolest recesses, shaped and 

 measured with strict reference to their adjacent shadows. A 

 considerable number of these interesting shadow-moraines are 

 still in process of formation, presenting a raw and rubbish-like 

 appearance, as if the boulders, mud, and sand of which they are 

 composed had been newly mined from the mountain's flank, 

 and dumped loosely from a car. Ancient shadow-moraines, 



