Water Supply of Kingston, Ont. 127 
These eleven samples were then compared as to their 
clearness, &e. No.1 was found to be the most free from 
suspended matter. Nos. 6, 9 and 11, were rather dirty. 
No. 4 also had considerable suspended matter. These 
results confirmed the evidence given by chemical analysis 
and by the experiments with floats. 
It may be of interest here to mention that my colleague, 
Prof. Marshall, has found that the temperature of the lake 
water is just now (Feb. 27) uniformly 32° F. from the ice to 
the bottom at a depth of 53 feet. This cooling of the deeper 
waters below the point of maximum density can hardly 
have been brought about by conduction alone. No doubt 
there has been considerable mixing of the top layers with 
the lower by means of the current. 
SoME LAURENTIAN RocKS OF THE THOUSAND 
ISLANDS. 
By Dr. A. P. Cotmman, School of Practical Science, Toronto. 
The Admiralty group of the Thousand Islands includes 
one hundred and fifty rocks, islets and islands extending 
two or three miles southwest of Gananoque. Two quarries 
and the bare glaciated flanks of the islands and the neigh- 
boring shore give excellent exposures of lower Laurentian 
rocks, here consisting of granite, gneiss and quartzite. 
Some dykes of fine grained diabase which intersect these 
rocks, though later than Laurentian are probably of pre- 
cambrian age, since they do not pierce the Potsdam sand- 
stone which overlies the eastern end of the group. 
Granite covers the largest surface and has invaded the 
gneiss and quartzite, sweeping off portions of them, gener- 
ally only a few inches or feet in diameter, but sometimes 
twenty feet or much more across. They are for the greater 
part quite sharp angled and uncorroded by the granite, and 
the quartzite fragments often stand out from the surface an 
inch or 80, giving a measure of the depth to which the gra- 
nite has weathered since the whole region was planed 
smooth in the Ice Age. 
“ 
