104 CHEMISTRY OF NATURAL WATERS. [IX. 



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

 first three trials, giving 2.5 per cent for the volume of water 

 which it is capable of holding in its pores, we find that a thick- 

 ness 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 a mean of 500 feet may be assumed. To this 

 are to be added 300 feet for the Calciferous sand-rock, 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. The capacity of the 

 800 feet of Chazy and Trenton limestones which succeed these 

 lower formations may be fairly taken at one half that of those 

 just named. But it is unnecessary to 'multiply such calcula- 

 tions : enough has been said to show that these sedimentary 

 strata include in their pores great quantities of water, which 

 was originally that of the palaeozoic ocean. These strata, through- 

 out the palaeozoic basin of the St. Lawrence, are now for the 

 greater part beneath the sea-level ; nor is there any good rea- 

 son for supposing them to have ever been elevated much above 

 their present horizon. "Wells and borings sunk in various 

 places in these rocks show them to be still filled with bitter 

 saline waters ; but in regions where these rocks are inclined 

 and dislocated, surface-waters gradually replace these saline 

 waters, which, in a mixed and diluted state, appear as mineral 

 springs. ' These saline solutions, other things being equal, will 

 be better preserved in limestones or argillaceous rocks than in 

 the more porous and permeable sandstones. 



17. .But besides the saline matters thus disseminated in a 

 dissolved state in ordinary sedimentary rocks, there are great 

 volumes of saliferous strata, properly so called, charged with 

 the results of the evaporation of ancient sea-basins. These 

 strata enclose not only gypsum and rock-salt, but in some 



