146 THE LAKES OF IOWA,—PAST AND PRESENT. 

















idly perhaps as it ever was, although only occasionally sub | 
ficient in amount to muddy the water. Thus it will be seen 
how slowly the mightiest operations of Nature are performed; 
for this most recent of the geological changes has doubtless 
required a length of time so great that the human mindis 
incapable of comprehending it. r 
In Northern Iowa the prairie horizons are not so clearly 
defined as they are farther to the southward, and it was 
doubtless so at the beginning. The drift also contains mo 
gravel and bowlders there, from the fact that nearly all of 4 
those materials originating still farther to the northward, 
their abundance diminished with the diminishing force of the 
glaciers to the southward. Numerous irregular rounded ele- 
vations or knobs mark the surface, between which are pit 
responding depressions; not produced however by erosion 
since the drift was deposited, as the river valleys were, bit 
are, like the knobs, inequalities left by the glaciers. wes 
Some of these depressions have become drained ; some of 
them are still occupied by the lakelets, and some by pe 
marshes. Streams are numerous in Southern Iowa, and ti : 
valleys deep. Consequently the country is so well drained 
and many of those lakelets still exist there, because noe 
cumulation of water beyond has sent a current across them 
to cut a channel for their outlet. Lake basins are sometime 
hollowed very deeply into the earth, showing bold exp? 
of stratified or unstratified rocks upon their shores. But : 
lakelets of which we are speaking, had their origin in shalo 
depressions left in the surface of the drift alone at tae 
of the Glacial epoch. By the action of subsequent 
they, in certain regions, became “walled lakes ;” for # 
ity of them are as worthy of that designation a8 those af" 
which the fanciful stories have been told. Nor aè? 
of that character confined to Iowa alone, but are know? 
in Minnesota, Wisconsin, Michigan, and even in Con? 
