﻿GEOLOGY OF THOUSAND ISLANDS REGION 69 



mere upper part of the whole, the giving of a local name seems 

 justified, and in Pamelia township the entire thickness is exposed. 

 As has been shown there is plain evidence of an erosion interval 

 between this and the Theresa, indicative of uplift to above sea 

 level and of erosion on this land surface. As will be later shown 

 this is an important and widespread break. The comparatively 

 slight amount of erosion is indicative of low altitude for this land 

 surface. 



The renewed depression which initiated Pamelia deposition 

 came in from the southwest' instead of from the east, involving 

 change in the direction of slope of the surface. 



The formation consists essentially of limestone, though much 

 of it is not pure limestone. It is conveniently separable into 

 lower and upper divisions which differ in lithologic character. 

 The lower division has always a sandy base, followed by alterna- 

 tions of black limestone, blue limestone and gray (somewhat 

 magnesian) limestone, often with shaly partings between the 

 beds. The upper division contains much whitish, earthy lime- 

 stone, with interbedded dove limestone and gray magnesian 

 limestone. The black limestone characterizes the lower, and the 

 earthy and dove limestones the upper division. 



In the western portion of the Theresa quadrangle the forma- 

 tion has a thickness of 150 feet or more. Traced eastward 

 across the quadrangle it thins considerably, and on the eastern 

 margin appears to have less than half this thickness though here 

 the drift is so heavy, and exposures so poor, that no good 

 measurements can be obtained. However, 60 feet seems a generous 

 allowance for the thickness here, and it is the beds of the lower 

 division which have disappeared. 



Following the formation westward, across the Clayton quad- 

 rangle to its disappearance beneath the river, the belt of outcrop 

 swerves somewhat to the north, and the formation thins somewhat 

 in this direction also. If it could be followed due west across the 

 quadrangle it would no doubt hold its thickness or even perhaps 

 increase. It is the northward shift that causes the thinning. A thick- 

 ness of at least 80 feet is maintained to the river however, and the 

 formation passes across into Canada with this amount not materially 

 reduced. The shore lines of this depositional basin then lay not far 

 distant to the east and north of the district and the invasion of the 

 sea must have come from the opposite direction. 



In the immediate district the formation rests everywhere on the 

 sandy dolomites of the Theresa. In the district about Kingston it 



