Lacustrine Deposits in the vicinity of the Great Lakes. 91 
The shore of Lake Michigan near this place, (Milwaukee, Wis- 
consin, ) consists of clay, sand, gravel and boulders, rising almost 
perpendicularly from fifty to one hundred feet. ‘The several lay- 
ers are usually arranged as follows: 
a, Hard-pan, or very tough blue clay with imbedded pebbles. 
b. Irregular beds of gravel, at some places fine, at others coarse, approaching 
boulders. 
ec. Very fine sand, free from pebbles or clay. Te P 
d. Fine reddish clay free from sand, pebbles, or boulders, having its base line 
nearly level. 
Along the line between a and 8, are numerous springs, usually 
of pure cold water, but occasionally impregnated with mineral 
substances. Some hold lime in solution in such quantities, as 
to cement the beds of gravel into a kind of pudding-stone, an 
incrust the moss, leaves, &c. over which they pass, affordin 
many fine and beautiful specimens. On the canal, half a mile 
above the city, is achalybeate spring issuing from a bed of gravel 
colored with the iron deposited by the water, 
Every storm-wind dashes the waves against the base of this 
steep bank, carrying away the light materials of which it is com- 
posed, and causing the higher portions to slide down as repre- 
sented in figure 1; an operation which is materially assisted by 
the springs above alluded to. This process is in some places 
quite rapid, and has been in operation for a great length of time. 
Many very interesting facts might be mentioned to illustrate this, 
and a few years of direct observation are suflicient to convince the 
most skeptical. ; 
A road laid out nine years ago on the bank of the lake, is now 
so near the margin that it would be impossible for a wagon to 
pass along it in the tracks then made, without falling down the 
slope. (See fig. 1,r.) Walking along the sandy beach of the lake, 
we often find the clay has slid down upon it, so that it 1s ne- 
cessary to clamber over the avalanche or wade around it in the 
waters of the lake. ‘These slides, under favorable circumstances, 
are very extensive, carrying down with them the forest trees 
without disturbing their erect position. At other times, trees 
throw wn towards the bank, presenting their roots to the 
‘water. At Southport, thirty-five miles south from Milwaukee, 
