OF THE NORTHWESTERN STATES. 25 



heavy slides, carrying with it trees, buildings, or whatever may be standing upon it. 

 Thin partings of sand near the water level assist in accelerating the process of de 

 struction. The fine materials thus taken from the land are, after a storm, suspended 

 for awhile in the water, which becomes colored and muddy several mUes from shore. 



In due time they are deposited at the bottom of the lakes, accumulating there 

 as a formation more recent than the drift, but reaching back to the close of the 

 drift period. The section at Cleveland illustrates the changes that have produced 

 this lacustrine alluvium. Lakes Erie and Michigan having a shore in most of its 

 circuit composed of the drift clays, are filling up more rapidly than Huron and 

 Superior, which have more rocky coasts. 



This deposit, as indicated by the mud found on a vessel, which sunk in sixty 

 feet water, three mUes off Cleveland, accumulates at the rate of more than twelve 

 feet in a century. It embraces the remains of man and of modern art. At the 

 city of Cleveland there exist data for an estimate of the rate of encroachment. 

 The site of the town was surveyed in 1 796. In 1842, forty-six years afterwards, 

 the advance of the shore line had been so rapid, that it was necessary to check it 

 by works erected ait the expense of the city, and afterwards made more permanent 

 by various railway companies. The encroachment opposite the public square since 

 the survey, had been, at that time, two hundred and sixty-five feet. 



Cleveland stands upon an inclined plateau sloping towards the lake at a rate 

 which would bring the shore down to lake level in about two mUes. Since the 

 lake assumed its present level, it has encroached thus far upon the land. Had it 

 continued to advance at the rate of the first forty-six years since the settlement of 

 the city, the coast line would, in about five hundred years, have reached the 

 public square on Superior street, and would have undermined the statue of Com- 

 modore Perry erected there. 



In 1796 the open mouth of the Cuyahoga river was at d, h, of the annexed 

 plan. Sometimes the west end of the old river bed was open and sometimes closed. 

 Before the end of five hundred years, at this rate, the mouth of the river would 

 have been at the foot of Superior street, and before the close of one thousand 

 years at F, f, near the Seneca street bridge. Soon after the shore line should have 

 reached Superior street, the bend of the river on Columbus street would have 

 formed a lagoon like those at c, c, c. 



On the Canada shore opposite Cleveland the rate of encroachment appears to be 

 as rapid, the height and composition of the shore being about the same. There 

 is in the blue clay a series of joints like those in the indurated rocks. When it 

 is undermined it falls in large blocks, with faces nearly at right angles. If it were 

 metamorphosed and hardened by heat, pressure, or chemical action, it would pre- 

 sent the external characteristics of the ancient azoic slates, being thoroughly lami- 

 nated and jointed. Here the slopes of the shore remained at rest, on an angle of 

 fourteen degrees inclination, but at other points they stand at a much steeper angle. 

 The color of the deposit now going on in the lake must be different from that of 

 the drift clays. On Lake Erie the silt brought down by rivers mingles with the 

 disturbed materials of the blue clay, giving it a more loamy character and a tinge 

 more brown and yellow. 



4 May, 1866. 



