10 THE CANADIAN NATURALIST. [Feb. 



dry air until they ceased to lose weight. They were then soaked 

 in distilled water, and kept under it for many hours beneath an 

 exhausted receiver. When thus saturated, they were wiped from 

 adhering water, and weighed ; first in air to determine the aug- 

 mentation of weight from absorption, and secondly, in water to 

 give, by the loss in weight, the volume of the specimens. These 

 data furnish the means of determining the volume of water ab- 

 sorbed, which is given below for 100.00 parts of different rocks 

 from the paleozoic strata of the St. Lawrence basin. 



Potsdam formation, (sandstone) 3 specimens.. 2.26 2.71 



" " " 3 " 6.94—9.35 



Calciferous " (crys. dolomite) 4 " 1.89 — 2.53 



" " " " 2 " 5.90— 7.22 



Chazy " (argil, limestone) 4 " 6.45-13.55 



Trenton " (grey crys. ") 4 " 1.18—1.70 



" " (black impalp. " ) 2 " 0.30 — 0.32 



Utica li (black shale) 3 u 0.75 — 2.10 



Hudson River " (arenac. " ) — 7.94 



Medina " (argil, sandstone) 2 specimens. .8.37-10.06 



Guelph " (crys. dolomite) 3 " .... 9.34-10.60 



Niagara " (impalp. " ) 2 " .... 9.69-10.92 



The above data might be much more extended, but sufficient 

 have been given to show the porosity of the principal paleozoic 

 rocks of the basin. * 



§ 16. If we take for the Potsdam sandstone the mean of the first 

 three trials, giving 25 per cent for the volume of water which it 

 is capable of holding in its pores, we find that a thickness of 100 

 feet of it would contain in every square mile, in round numbers, 

 70,000,000 cubic feet of water; an amount which would supply 

 a cubic foot (over seven gallons) a minute for more than thirteen 

 years. The observed thickness of the Potsdam sandstone in 

 the district of Montreal, varies from 200 to 700 feet, and the 

 mean of 500 feet may be taken. To this are to be added 300 

 feet for the Calciferous formation, whose capacity for water may 

 be taken, like the Potsdam sandstone, at 2*5 per cent. We have 

 thus in each square mile of these formations, wherever they lie 

 below the water-level, a volume of 490,000,000 cubic feet of 

 water, equal to a supply of a cubic foot per minute for 106 years. 



* A great many similar determinations will be found in a Report on 

 Building Stones to the British House of Commons in 1839, by Barry, 

 JDelabeche, and Smith. See also Delesse, Bui. Soc. Geol. [2] xix, 64. 



