J. LeConte—Ancient Glaciers of the Sierras. 327 
there, these surfaces, although so comparatively recent, are only 
found in patches. A few hundred or thousand years will prob- 
ably remove every vestige of them, except where protected by 
soil. Glaciated forms, on the contrary, are much more perma- 
nent; but these are most conspicuous always in the bed of the 
glacier ; and there they are apt to be covered up, after the re- 
treat of the glacier, by lake deposits and by debris brought by 
tributary glaciers coming down through side cafions. In the 
Yosemite the glacial bed rock has been entirely covered up by 
these means, particularly by lake deposits, which are here very 
conspicuous. So far as glaciated forms and surfaces are con- 
cerned, therefore, only the walls remain to tell the story. 
r. Muir first drew my attention to the fact that the almost 
perpendicular walls of Yosemite are in many places absolutely 
ree from talus, the hard, smooth rocky wall coming down 
directly to the level meadow soil of the valley. In every such 
place the wall rock is found to be very hard and solid, more 
or less projecting and rounded, with a gentle slope on the side 
looking up the valley, and with a more abrupt curve or even 
broken on the lower side; in other words it is a true moutonnée 
form. Other parts of the wall are irregular and destitute of 
glacial signs ; but the reason is evident in tlie piles of debris at 
the bottom. The former consist of hard material, little affected 
by joints, and have, therefore, remained in the condition in 
which the glacier left them ; the latter consist of softer materials, 
and have crumbled and thus destroyed the glacial signs since 
the period of glacial occupation. Thus, on the north side of 
the valley every projecting shoulder is rounded and smooth 
and without talus, while every re-entering angle is rough and 
Jagged, and has its pile of debris at its base. In some cases, as 
for example high up on Washington column, the smoothness of 
these projecting shoulders is such that they glisten in the sun- 
shine. TI believe if these spots could be reached they would be 
found scratched and polished. 
ese moutonnée forms are found principally on the north 
wail. The reason is evident. In an east and west chasm so 
€ep, so narrow, and with walls so perpendicular as this, the sun 
shines with full effect only on the northern wa nerefore ice 
and snow and small tributary glaciers hung about the cliffs and 
side-cafions, on the south side, long after the retreat of the 
Main glacier, and after the northern wall was entirely clear. 
Under the disintegrating influence of this frost, the glaciated 
forms and surfaces produced by the main glacier have been en- 
tirely destroyed on the southern wall. 
Again: although the old terminal moranies are not so clear 
a8 might be desired, yet I think no one who was examined the 
glacial valleys of the Sierras, and thereby made himself thor- 
oughly familiar with the appearance of half-effaced moraines, 
