and Spouting Fountains. 21T 



ken and detached ; so that some of them are exposed and crop 

 out on the sides and summits of the hills. This phenomenon 

 may be represented wjth sufficient accuracy by folding a quire 

 of writing-paper upon the edge of a paper cutter. When put 

 into this position, as when lying on the table, the upper sheet 

 covers the whole of the second, and the second the whole of the 

 third, and so on. But let us now tear the quire towards the 

 angle we have made, and let us trace this tear through ten or a 

 dozen of sheets, and, as is apparent, each of these sheets be- 

 comes visible, and all will be exposed directly to atmospheric in- 

 ftuences. 



We find, in the series of strata, of different kinds, which, al- 

 ways arranged in a given order, go to form the tertiary series, 

 beds of permeable sand, in many elevations. The surface water 

 must run through them, first in the portions where the in- 

 clination is great, because of the weight of the water ; and then 

 in the horizontal branches, oft account of the pressure exercised 

 by the water which the remaining portion of the bed has not 

 allowed to escape. It might be only right, therefore, to expect, in 

 every locality, to find embosomed in each more solid tertiary 

 formation, as many subterranean sheets of water as we can find 

 distinct successions of sand-beds reposing upon impermeable 

 strata. 



So far, then, as regards the circumstances under which these 

 subterranean waters may be found, there seems to be an entire 

 correspondence between the secondary and tertiary formations, 

 however much they may differ in other respects, so as to require 

 a distinct classification at the hands of the geologist. We shall 

 take occasion to point out, on this occasion, only a single differ- 

 ence, to which M. Jules Burat has already directed the atten- 

 tion of civil-engineers, in the excellent memoir which he has 

 published on the subject. It is this fact — that in the secondary 



formation of higher antiquity. In this latter case, the diffei-ent beds of more 

 recent deposition extend horizontally, till they come in contact with the 

 older rocks, which enclose them as in a circus. The upper bed is only visible, 

 and it alone directly receives the descending rains ; the surface water can- 

 not reach the older strata, except across the beds which cover it ; conditions 



which are little favourable to the formation of subterranean lakes, at least 

 when compared with those which exist in basins, the bounding ridge of whicli 

 is composed of strata which have undergone the alterations above alluded to. 



