MOHAWK LAKE BEDS. 
395 
Sierra had retreated from their most advanced position; but 
their testimony goes no farther. The narrow range of levels 
common to the two may have been occupied first by ice and 
afterward by the water, or it may have been occupied by 
both together. We can only say that the ice was first to 
retreat. 
“ Combining this result with that afforded by the moraines 
of the Bonneville basin, we conclude that the epoch of great¬ 
est glaciers fell within the second period of lake expansion, 
but did not coincide with the epoch of greatest water supply. 
It occurred somewhat earlier. If the two sets of phenomena 
were consequent upon the same series of climatic changes, 
then the lacustral changes lagged behind the glacial. 
“That such a lagging admits of plausible explanation 
may readily be shown. The neve and glaciers of the Mono 
district occupied a portion of the catchment basin of the 
lake. The precipitation which they accumulated during 
their growth was subtracted from the precipitation tributary 
to the lake, and the same was afterward returned to the lake 
when they were finally melted. Their mass of ice may 
therefore be regarded as a portion of the water supply of 
the lake, arrested in its progress. When the climatic con¬ 
ditions were favorable for the growth of lake and glaciers 
the growth of the glaciers antagonized and delayed the 
growth of the lake. When the climatic conditions favored 
the wasting of lake and glaciers the waste of the glaciers 
fed the lake and thus antagonized its depletion. The ascend¬ 
ing and descending phases of the lake thus fell behind the 
corresponding phases of the glaciers, and the maxima and 
minima or turning points were correspondingly displaced. 
“ It is to be observed that this explanation is quite distinct 
from the theory, alluded to by Whitney (XVIII, page 185), 
that the Pleistocene lakes were the sequel of the Pleistocene 
glaciers, being created by their melting. Such a relation is 
quantitatively impossible. In the Mono basin, indeed, the 
mass of snow and ice upon the mountains may have been 
equal 1 6 the volume of water in the valley, but in the La- 
hontan and Bonneville basins it was far too small.” 
