92 Lacustrine Deposits in the vicinity of the Great Lakes. 
the bend of a stream has been car- Fic. 2 
: g. 2. 
ried away, so that its valley pre- 
sents three openings to the lake, C d 
as represented in figure 2, where on ty, eNO ak 
the dotted lines represent the an- (Sy 
cient state of things and the black fy 
ines the modern. Similar in- --—! tm 
stances may be observed at other ; 
places along the shore of the @ Ancient coast.—b. Present coast. 
ot —d. 
lake. ite 
River. 
The prevailing storm-winds here are from the northeast, stri- 
king the coast obliquely and carrying the gravel and sand acted 
upon by the waves in a southerly direction, or towards the head 
of the lake. The progress of the pebbles along the shore is slow, 
each storm carrying them but a small distance ; yet the constant 
action of the waves through a long period of time, has been suffi- 
cient to accumulate vast fields of sand around the southern ex- 
tremity of the lake. When a solid pier is built into the lake, this 
motion of the sand and pebbles causes a rapid accumulation on 
the north side of it. At Chicago, during five years, the accumu- 
lation of sand extended no less than seven hundred and twenty 
feet along the pier. As soon as the sand reaches the end of the 
pier, a bar is formed across the mouth of the harbor, rendering 
another “appropriation” necessary to extend the pier further into 
the lake. How far it will be necessary to extend the pier before 
the difficulty will cease, is not easily determined. It will be 
when the direction of the shore north of the pier is at right angles 
with the direction of the prevailing storms. Figure 3 represents 
the shore at this place in the different years from 1834 to 1839, 
1s copied from an official report of the Topographical Bureau 
at Washington. Since 1839, no reports have been made. 
Fig. 3. 
@. The original shore.—b. Shore in 1835.—c. Shore in 1836,—d. Shore in 1837. 
—¢, Shore in 1838.—f, Shore in 1839.—G. North pier. ao 
