i84 



Sierra Club Bulletin 



millionth part of which is now to be seen ? It has not been engulfed, 

 because the bottoms of all the dividing valleys and basins are unmis- 

 takably solid. It must, therefore, have been carried away; and be- 

 cause we find portions of it scattered far and near in moraines, eas- 

 ily recognized by peculiarities of mineralogical composition, we in- 

 fer that glaciers were the transporting agents. That glaciers have 

 brought out the summit peaks from the solid with all their imposing 

 architecture, simply by the formation of the valleys and basins in 

 which they flowed, is a very important proposition, and well deserves 

 careful attention. 



We have already shown, in studies Nos. Ill and IV, that all the 

 valleys of the region under consideration, from the minute striae 

 and scratches of the polished surface less than a hundredth part of 

 an inch in depth, to the Yosemitic gorges half a mile or more in 

 depth, were all eroded by glaciers, and that post-glacial streams, 

 whether small glancing brooklets or impetuous torrents, had not yet 

 lived long enough to fairly make their mark, no matter how un- 

 bounded their eroding powers may be. Still, it may be conjectured 

 that preglacial rivers furrowed the range long ere a glacier was born, 

 and that when at length the ice- winter came on with its great skyfuls 

 of snow, the young glaciers crept into these river channels, overflow- 

 ing their banks, and deepening, widening, grooving, and polishing 

 them without destroying their identity. For the destruction of this 

 conjecture it is only necessary to observe that the trends of the pres- 

 ent valleys are strictly glacial, and glacial trends are extremely dif- 

 ferent from water trends; preglacial rivers could not, therefore, 

 have exercised any appreciable influence upon their formation. 



Neither can we suppose fissures to have wielded any determining 

 influence, there being no conceivable coincidence between the zigzag 

 and apparently accidental trends of fissures and the exceedingly 

 specific trends of ice-currents. The same argument holds good 

 against primary foldings of the crust, dislocations, etc. Finally, if 

 these valleys had been hewn or dug out by any preglacial agent 

 whatever, traces of such agent would be visible on mountain masses 

 which glaciers have not yet segregated; but no such traces of valley 

 beginnings are anywhere manifest. The heads of valleys extend 

 back into mountain masses just as far as glaciers have gone and no 

 farther. 



Granting, then, that the greater part of the erosion and transpor- 



