298 Tertiary. 



5th. "Lacustrine deposits," occupying the basin of the lakes, and 

 for Lake Erie, divided into the " blue marl}' sand," and the coarse sand 

 and gravel. The " blue marly sand," commonh' called the blue clay of 

 Lake Erie, is seen skirting the shore almost ever3'where, if the coast is 

 not rocky, — its upper face nearly horizontal, and rising from forty-five 

 to sixty feet above the water. It is of a light blue color, so fine as 

 scarcely to show between the fingers any grit, homogeneous, and in a 

 dr^' state compact, but brittle. Very rarely, may be seen a primitive 

 pebble, thin layers of leaves and lignite. It is distinctly and liorizon- 

 tally laminated, and at Cleveland is composed of about 75 per cent, im- 

 palpable sand, 3 per cent, iron, 6 to 7 per cent, carbonate of lime, 9 per 

 cent, carbonate of magnesia, and of vegetable matter and sulpliur. It 

 is impervious to water, and thus causes thousands of springs to ap- 

 pear at its surface, which, passing out over the edges, dissolve and 

 carry it away ver}' fast, forming a quick sand. Its edge is presented 

 to the action of the waves, which dissolve and carry it away rapidly. 

 As it is not tenacious like clay, and not capable of sustaining itself 

 under its own weight, and that of the sand stratum that rests upon it, 

 there are continual breaks and slides along the banks, on both the 

 American and Canadian shores. These avalanches of earth ai-e from 

 one to four rods in width, breaking oflf in irregular patches, and some- 

 times sinking, in a night or in a few hours, twenty or thirt}' feet, leav- 

 ing huge fissures through which the water of the springs passes, and 

 rapidly washes the earth into the lake. 



At the water's edge, the slide frequentl}' raises a bank of about the 

 width of the break, several feet above the surface, driving back for a 

 short time the line of the shore. But the waves acting incessantly 

 dissolve the new barrier, and soon commence their attacks upon the 

 body of the fallen mass, which disappears, and is before long followed 

 by a fresh avalanche from above. 



At the cit}^ of Cleveland, where the bluff" shore rises 70 feet above 

 the lake, the encroachment since the survey of the town in 1796, has 

 been at the foot of Ontario street, 265 feet. The Canadian shore, from 

 Detroit river to Long point, is losing faster than the American. Be- 

 tween Port Stanley and Port Burwell, on the British side, the superior 

 face of the blue marl is about sixty feet, or fifteen feet higher than at 

 Cleveland, and has in the upper part a lighter or more yellow color. In 

 composition the yellowish portion is more argillaceous than the bright 

 blue, and appears to correspond with the 3'ellow clay stratum of Lake 

 Champlain, The gi'eatest thickness of the blue marls can not be com- 



