130 CHAMPLAIN DIVISION. 



to the soil. In this lospect thoy ;irc dissimilar to the primary and magnesian limestones, 

 which cnimUK', and frequently form around their beds from twelve to twenty inches of 

 comminuted calcareous earth. Another feature in the limestone, and even in the Potsdam 

 sandstone, is its fissured state. The natural joints at the surface are opened widely, so as 

 to admit the falling of large bodies into them ; and into these cracks or fissures the surface 

 water (lows freely, and for this reason some portions of the country are liable to suffer from 

 drought. But this is not all. Few if any springs issue from these rocks, except at a low 

 level ; and hence we find very frequently the waters which have been swallowed in the 

 deep fissures, flowing out of the banks of some stream. The limited extent, however, of 

 these fissured rocks, does not affect very materially the agricultural products : they are not 

 barren in consequence of a want of water, as are some large limestone tracts in the State of 

 Kentucky. 



Upon the whole, the country underlaid by the Champlain division is favorable to agri- 

 culture. The slopes are rarely steep ; the hills are susceptible of cultivation to their tops, 

 and the disposition to produce grass of a sweet kind renders the fields and hillsides favorite 

 grounds for the pastiuage of flocks. The slates and shales are much less fissured than 

 the limestones and sandstones ; and, hence, from the impervious nature of their beds, they 

 prevent the rapid escape of surface water. This holds good, whether the slates are hori- 

 zontal or raised to a steep inclination ; for, in the latter case, the laminae are so powerfully- 

 pressed together, that if any thing they become more impervious than the undisturbed beds. 

 However, where the rocks are horizontal, or even inclined, they always admit of an easy 

 drainage ; for ravines occur wherever there is a stream of running water, and these form 

 general drains, into which artificial ones may be opened over the whole country where 

 these rocks prevail. 



§ 13. Springs which issue from the members of the champlain division. 



It is not possible always to determine the source of a spring, unless indeed the rock itself 

 is sufficiently exposed to observation. A spring issuing immediately from the soil, may, 

 previous to its exit, have traversed the rocky strata from a great depth ; or it may only have 

 percolated to an inconsiderable depth into the soil, and meeting an impervious stratum, it 

 is soon forced again to the surface. If it passes through sand and gravel, it remains nearly 

 pure ; but if, on the contrary, it passes through shales or slates, charged with pyrites, with 

 lime and saline matters, it dissolves a portion of them, and becomes in consequence what 

 is termed a mineral spring. Its temperature too will suffer some change : if it percolates 

 through fissures to a great depth, it will be raised. Every sixty feet,* in this country, will 

 impart a degree of temperature. It may, however, lose a portion of its temperature in its 

 upward passage. By far the greater number of springs issue from the earth at a tempera- 

 ture al)ove the mean of the place. 



The composition of the water of a spring is evidently affected by the strata through which 



* This holds good only below the line of no variation. 



