GLACIERS OF THE SIERRA COSTA MOUNTAINS 43 
open U-shaped trough, with smooth and curved slopes, and a 
gently rounded floor. This change has been effected by a 
grinding away of the talus material and solid rock along the 
middle levels of the slopes and a filling of the extremely narrow 
lower portion of the gulch. The ravines have been destroyed, 
partly by filling and partly by the grinding away of the inter- 
vening ledges. Often this smoothing of the contours has 
extended up toa certain level, above which the mountain sides 
are deeply scored with ravines, and jagged with outcropping 
ledges. 
Most of the valleys present but a moderate amount of ground- 
moraine, altho the lateral moraines are well developed. The 
glaciated slopes are abundantly supplied with bowlders of all the 
rock species occurring from thence to the head of the valley. 
They are embedded in a loose agglomeration of subangular 
gravel, sand and a little clay, forming a deposit quite unlike the 
till of the Mississippi basin, altho somewhat more nearly resem- 
bling the very stony moraines of New England. These lateral 
moraines are smooth in outline, rarely displaying a hummocky 
topography, and only in a few cases standing out distinct from 
the mountain ridges. In the unglaciated gulches, especially 
‘where the country rock is serpentine, extensive land slips are 
resting on the lower slopes, and they present a hummocky 
topography almost identical with that so characteristic of glacial 
moraines in the Mississippi basin, even to the extent of possess- 
ing kettle-holes containing lakelets. These must not be con- 
founded with the lateral moraines. 
Lines of erratics perched high on the mountain sides some- 
times indicate the maximum altitude of the glacial action. From 
the smooth curved slopes of the lateral moraines, low narrow 
ridges of very stony material trend obliquely toward the center 
of the valley, those on opposite sides forming a loop, pointed 
downward. Sometimes they coalesce and are then cut by a 
small canyon-shaped valley thru which the stream finds an outlet 
from the enclosed basin above. These are the only representa- 
tives of true terminal moraines (being formed at successive 
