314 



SPRINGS PRODUCED BY VALLEYS AND SLIPS. 



gives rise to so many natural springs, and enables us by artiBcial wells 

 to bring water to the surface — often where the land would otherwise be 

 wholly uninhabitable.  



3°. Thus in undulating countries, where hill-sides frequently pre- 

 sent themselves, or valleys are scooped out among the rocks, as in the 

 following wood-cut, the water that has fallen over the high grounds to- 



wards A, and has entered as above described, or has sunk down to the 

 several strata 1, 2, 3, &c., will find a ready outlet along the slojje of tlie 

 valley, and will give rise to springs at a, b, c, or d, according as the wa- 

 ter has lodged in the one or the other of these beds. These springs will 

 fill the surface soil with water, which will also descend into the botiom of 

 the valley, and, if no sufficient outlet be provided for it, will, according 

 to its quantity, give rise to a lake, a bog, or a morass. On the slope to- 

 wards B the same springs are not to be expected, since the rains which 

 sink through the surface on this side of the valley, and lodge in the po- 

 rous rocks beneath, will, by the inclination of the beds, be drawn off in 

 the opposite direction, till a second valley or some other available outlet, 

 present itself for their escape. This explains why the land on one side 

 of a valley or of a hill is often much drier than on the other, and why, 

 even in the absence of the improver's skill, an apparently more fertile 

 soil may exist, and betler crops.be reaped. 



4°. Again, such an outlet for the waters that rest among inclined strata 

 is not unfrequently afibrded, without the intervention of valleys, and 

 even in level or hilly countries, by the existence of slips or faults in the 

 rocks beneath. Such a slip or shifting of the beds is represented in the 



annexed diagram, in which B D is a crack, along which the strata from 

 B to C appear to have slipped downwards, so that the thin bed (2), for 

 example, which terminates at b on the one side of the crack, begins again 

 at a lower level c on the other side, and so with the other beds that lie 

 above and below it. None of them is exactly continuous on the oppo- 

 site sides of the slip. From such cracks or faults in the beds, springs of 

 water often rise to the surface, even on hill tops, as at B, and they may 

 be thus thrown or forced out from either of two causes — 



1. These slips are often of considerable width, and arfe usually found 

 to be filled with impervious clay. This is the case at least among the 

 coal measures, which have beeu the most extensively explored. The 

 effect of this wall of clay is to dam back at B D the water which de- 



