or THE NORTHWESTERN STATES. 27 



Most of tlie shore of Lake Michigan is sandy, bnt in part it is of blue, purple, 

 and red clay (see profiles at and near Milwaukee). At Cleveland, some deceased 

 soldiers of the war of 1812 were buried near the margin of the bluflf, and in 1836 

 their remains had already reached the lake level, under the operation of repeated 

 slides. A short time prior to 1796 a British vessel was wrecked within the present 

 limits of the city of Cleveland. There were on board of it some brass field pieces, 

 which were taken out by the captain, and buried on a bench about half way up 

 the bank. These pieces have often been sought for without success. The encroach- 

 ment of the water line must have reached them in about twenty years, when they 

 would soon settle into the soft clay and quicksand out of sight. The rate of 

 advance is, however, not imiform ; it depends upon the character of the materials 

 and the height of the water. By consulting the Smithsonian Contributions for 

 1860, vol. XII., it wiU be seen that all the lakes are subject to fluctuations of level 

 varying from five to seven feet. During periods of low water, the wearing action is 

 not rapid. There are times for many years together when there is a beach of 

 littoral sand, along the foot of shore bluffs previously washed by the waves. 



The early emigrants to Ohio had the good fortune, from 1796 to 1800, to find a 

 natural road along the beach of Lake Erie, which was soon after submerged. By 

 turning to the profile along Bank street, Cleveland, page 26, the process of under- 

 mining and consequent removal of the shore bluffs will be rmderstood. There are 

 no rocks indeed so solid but that the action of the surf destroys them more or less 

 rapidly. Where the shore has no rocky barrier, but only a bank of clay, or of clay 

 interstratified with sand and gravel, the work of destruction is rapid. AU the 

 drift clays are marly, and also contain sand in a fine state of division. The water 

 softens, and dissolves these marly clays into a quicksand. 



A very slight motion of the water is sufficient to carry away this material, the 

 coarser parts and the gravel remaining on the beach, while the finer parts go to form 

 alluvium at the bottom of the lake. When the undermining process at the water 

 line has reached so far as to destroy the equilibrium of that kind of earth, there 

 must be a slide. The weight of the earth at the summit of the bluff carries it 

 downward in long narrow strips of land, one, two, and three rods wide, according 

 to the height of the shore. This movement, somewhat like a crevasse, pushes the 

 mass of previous slides, C, C, C, forward and downward into the water. Excava- 

 tions on the sides of the valley of the Cuyahoga river show the fissures of very 

 ancient slides. 



The movements are easily traced by the position of the different strata B, C, D, 

 which differ both in color and composition. 



A mere line marks the crack along which the slide moved in its descent, unless 

 the waters of the springs enter it, and disintegrate the beds. Some of the fissures 

 are open, particularly at the base of the slides, and some are filled with oxide of 

 iron deposited from solution. We have here cases of faults and dislocations oc- 

 curring before our eyes, where the opposite surfaces are smooth, and scarcely dis- 

 cernible. 



As the red clay is more tenacious than the blue, it stands at a steeper angle, but 

 the coast-line of Lake Superior is gaining upon the land with equal rapidity. The 



