570 WILLARD D. JOHNSON 



two extreme views indicated; namely that, as regards quantitative 

 effects in degradation more especially, glaciation had been widely 

 destructive of the preglacial topography, on the one hand; on the 

 other, that it had been relatively protective. But there was no rec- 

 ognition of distinctive forms — beyond "U-canyons" and moraines. 

 I had little notion, therefore, as to what I should discover; only an 

 open mind and a lively curiosity. 



I was a maker of topographic maps, of some experience, and had 

 a topographer's familiarity with the erosion aspects of mountains; 

 but only of unglaciated mountains I had as well, however, some- 

 thing of the inquisitiveness of the physiographer as to the origin and 

 development of topographic forms. 



The first station occupied in this work of survey was Mount 

 Lyell, one of the most widely commanding summits of the vast 

 mountainous tract of the High Sierra. 



From Lyell there was disclosed a scheme of degradation for which 

 I had not been in the least prepared. No accepted theory of erosion, 

 glacial or other, explained either its ground-plan outlines or its canyon- 

 valley profiles; and, so far as I can see, none makes intelligible its 

 distinctive features now. The canyons, at their heads, were abnor- 

 mally deep; they were broadly flat-bottomed rather than U-formed, 

 the ratio of bottom width to depth often being several to one; and 

 their head walls, as a rule, stood as nearly upright, apparently, as 

 scaling of the rock would permit. I characterized them, figuratively, 

 as "down at the heel." In many instances the basin floor, of naked, 

 sound rock in large part, and showing a glistening polish on wet 

 surfaces, was virtually without grade, its drainage an assemblage of 

 shallow pools in disorderly connection; and not infrequently the 

 grade was backward, a half-moon lake lying visibly deep against the 

 curving talus of the head wall, and visibly shallowing forward upon 

 the bare rock-floor. 



The amphitheater bottom terminated forward in either a cross- 

 cliff or a cascade stairway, descending, between high walls, to yet 

 another flat. In this manner, in steps from flat to flat, commonly 

 enough to be characteristic, the canyon made descent. In height, 

 however, the initial cross-cliff at the head dominated all. The tread 

 of the steps in the long stairway, as far as the eye could follow, greatly 



