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Sierra Club Bulletin. 



water erosion — on early and strong grades. The cirque 

 hollow was a true amphitheater; its walls, or precipitous 

 slopes, descended, not to a funnel-point, but to a floor, 

 approximately level. And the breadth of the amphi- 

 theater on its floor commonly exceeded even the imposing 

 measure of its depth. 



The basins about which the cirques were ranged as 

 alcoves, each contained a central draining canon. In 

 each, tributary canons, starting at the cirques, converged 

 toward this central canon-head, rapidly shallowing and 

 entering at high levels.* It is this point of drainage 

 convergence in the basin which more properly corre- 

 sponds, perhaps, to the funnel-point of the miniature 

 bad-land form. 



Within the basins, — ^that of the Tuolumne, which I 

 had followed to Lyell, and others subsequently visited, — 

 all surfaces were glaciated, exhibiting abundant polish, 

 striae, and moutonnee details. Only the crests, with their 

 occasional tabular elements, were free from these evi- 

 dences. Postulating glaciation, the serrate ridges and 

 the high tables alone had been emergent from the 

 Pleistocene ice ; the basins had been **neve fields" ; and 

 the central canons, channel troughs of glacial escape. 



Migration of the divides by cirque-wall recession, 

 with accompanying degradation of a thousand feet or 

 more, was to be inferred; but, on the other hand, were 

 the central canons of the basins wholly preglacial, and 

 merely cleared out? 



The troughs at their heads were abruptly deep, often 

 profoundly deep. To notable distances their floors, start- 



* Such a canon head, central to a meander arc of the divide, is developed 

 in type form in the basin of the Merced, five miles southwest of Lyell. 



