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Sierra Club Bulletin 



glaciation of the most comprehensive kind, and present noble 

 illustrations of the physical and climatic conditions under 

 which the Sierra lay when all the sublime pages of her his- 

 tory were sealed up. The lofty Himalaya, the Alps, and the 

 mountains of Norway are more open, their glacial covering 

 having separated into distinct glaciers that flow down their 

 valleys like rivers, illustrating a similar glacial condition in 

 the Sierra, when all her valleys and cafions formed channels 

 for separate ice-rivers. These have but recently vanished, 

 and when we trace their retiring footsteps back to their 

 fountains among the high summits, we discover small resid- 

 ual glaciers in considerable numbers, lingering beneath cool 

 shadows, silently completing the sculpture of the summit peaks. 



The transition from one to the other of these different 

 glacial conditions was gradual and shadow-like. When the 

 great cycle of icy years was nearly accomplished, the glacial 

 mantle began to shrink along the bottom ; domes and crests 

 rose like islets above its white surface, long dividing ridges 

 began to appear, and distinct glacier rivers flowed between. 

 These gradually became feeble and torpid. Frost-enduring 

 carices and hardy pines pushed upward along every moraine 

 and sun-warmed slope, closing steadily upon the retreating 

 glaciers, which, like shreds of summer clouds, at length dis- 

 appeared from the young and sunny landscapes. 



We can easily understand that an ice-sheet hundreds or 

 thousands of feet in thickness, slipping heavily down the 

 flanks of a mountain chain, will wear its surface unequally, 

 according to the varying hardness and compactness of its 

 rocks; but these are not the only elements productive of 

 inequalities. Glaciers do not only wear and grind rocks by 

 slipping over them, as a tool wears the stone upon which 

 it is whetted; they also crush and break, carrying away vast 

 quantities of rock, not only in the form of mud and sand, 

 but of splinters and blocks, from a few inches to forty or fifty 

 feet in diameter. 



The whole mass of the Sierra, as far as our observation 

 has reached, is built up of brick-like blocks, whose forms 

 and dimensions are determined chiefly by the degree of 

 development of elected planes of cleavage, which individualize 



