﻿GEOLOGY OF THOUSAND ISLANDS REGION Jl 



succeed alternations of blue limestone and gray, magnesian lime- 

 stone, with occasional white; earthy beds, and with thin recur- 

 rences of the blackish limestones with traces of the marine fauna; 

 in the other beds the fossils are chiefly, or exclusively, ostracods. 

 As the formation thins to the east and west the lower gray beds 

 disappear, bringing the basail sands up under the black limestone 1 

 with further thinning this disappears in its turn, but at the same 

 time the higher black layers seem to show increased thickness and 

 prominence, so that where the lower division has been thinned to 

 a few feet, as it has over much of the region, it is still character- 

 ized by black, fossiliferous limestone. 



This lower division has a measured thickness of 70 feet in a 

 nearly complete section by Perch lake. It is likely somewhat 

 thicker to the west but probably does not exceed this more than 

 15 or 20 feet. A well near Stone Mills was drilled 125 feet in 

 the formation without reaching the base, but drilling commenced 

 in the upper division and how large a part of that is involved is 

 not known, though likely 50 feet must be allotted to it. 



The upper division consists of alternations of white earthy lime- 

 stone, and of dove limestone, with occasional beds of gray, and of 

 blue, hard, subgranular or subcrystaHine limestone; there is also 

 some yellow, earthy limestone, and a horizon where a reddish tinge 

 is likely to prevail. The summit is chiefly of dove limestone. The 

 earthy limestones hold numerous nodules of coarsely crystalline 

 calcite, which attain quite large size in some of the upper layers, 

 with diameters of from 3 to 5 inches. Celestite nodules also occur, 

 but much less frequently. Much of the upper division is thin 

 bedded, weathering into small, yellow stained slabs an inch or two 

 in thickness; and the stone walls of this thin material which line 

 the roadsides and separate the fields everywhere characterize the 

 upper Pamelia country. 



The surfaces of many of the layers are covered with shrinkage 

 cracks, especially in the upper part of the division. Sand grains 

 also appear in some of the- white, earthy beds. Abundant Stylio- 

 lites occur at certain horizons in the upper dove limestones. The 

 evidence of estuarine, or lagoon deposition, with evaporating 

 waters, occasional exposure of broad mud flats, and from time to 

 time replenishment of the water from the sea outside, freshening 

 it and bringing in traces of the outer marine fauna to mingle with 

 the ostracod fauna of the lagoon, is very plain and conclusive ; 

 prevalence of somewhat arid climate is also suggested. The rock 

 is very like, and the climatic and depositional conditions very simi- 



