a 
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 te- 
moved dows 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 sun, took advantage of his newly ae- 
‘ged freedom, and hopped off, with much apparent satisfaction. 
_ Lake Erie is somewhat similarly situated, in as much as the 
oor of its basin, and the barrier at its cette are formed by the 
mountain limgatone, But, instead of lying at right a 3 to” 
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 mouintaiti 
limestone, which, in 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. 
Before this limestone terrace had become sufficiently eleveiial 
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~ 
see. and found its exit seboge the valet of the Mohawk 
a A 38, 
1 Dr. Bigsby, American Journal, Vol. vis. PTB a 
