94 Geology and Topography of Western New York. 



The same thing occurs in many of the valleys, but on a vastly 

 larger scale ; the shale and sandstone being cut through and re- 

 moved down to the surface of the mountain limestone, as before 

 stated. In cases like this, the latter rock, at its northern outcrop, 

 forms a barrier across the mouths of such valleys. The streams 

 which flow into them, are obstructed at these points ; and lakes 

 of greater or less magnitude result. All of those whose outlets 

 are situated on the line of bearing of the limestone strata, which 

 extends from the Niagara to the Hudson rivers,* as Canandaigua, 

 Seneca, Cayuga, Skaneateles, and some of the smaller lakes, 

 doubtless owe their origin to this peculiar feature in the dip and 

 arrangement of the strata. Other valleys, also, in this range, 

 were probably once occupied by lakes. In that of Bristol, the 

 depth of the alluvium is unknown. In sinking wells, trunks of 

 trees are met with at considerable depths ; and in one instance, a 

 frog is said to have been dug up, which, on being exposed to the 

 vivifying influence of the sim, took advantage of his newly ac- 

 quired freedom, and hopped off, with much apparent satisfaction. 



Lake Erie is somewhat similarly situated, in as much as the 

 floor of its basin, and the barrier at its outlet, are formed by the 

 mountain limestone. But, instead of lying at right angles to the 

 bearing of the strata, it occupies a basin at the junction of the 

 shale and limestone, formed by the removal of the outcropping 

 edges of the former. Its longitudinal direction, therefore, has a 

 general coincidence with the line of bearing of the strata ; and 

 its northwestern shore, consequently, is formed by the mountain 

 limestone, which, m that direction, attains an elevation above 

 the surface of the lake, and underlies the peninsula in Upper 

 Canada, included between Lakes Erie, Ontario, Simcoe and 

 Huron.f 



Before this limestone terrace had become sufficiently elevated 

 to shut out the sea from the basins now occupied by these lakes, 

 their shores were swept by its waves, and they differed in no 

 material features, from the estuaries of rivers, or the bays which 

 indent our sea coasts at the present day. It is highly probable, 

 also, that a strong current set in through the Gulf of St. Law- 

 rence, and found its exit through the valleys of the Mohawk and 



* Prof. Vanuxem, New York Geological Report, 1838, p. 272. 

 \ Dr. Bigsby, American Journal, Vol. vui. p. 78. 



