204 GEOLOGICAL DISTURBANCES. 



It cannot penetrate and sink farther, so it follows 

 along this layer, till it comes out above c, on the side 

 of the hill, and wets all of the country below. On 

 the other hill a, if the strata are pervious to water, it 

 will all sink away, and the soil will be perfectly dry. 



SECTION III. OF THE CAUSES WHICH HAVE DISTURBED THE 

 REGULAR FORMATION OF SOILS, FROM THEIR UNDERLY- 

 ING ROCKS. 



From the foregoing explanations, it might be sup- 

 posed, that if we know the rock lying underneath any 

 given field, and can tell of what that rock is composed, 

 we may be able to decide positively upon the charac- 

 ter of the soil on the surface. This is not, however, 

 always the case. 



That it is not so, may be ascribed to the numerous 

 convulsions of the earth's surface, which have been 

 before mentioned. Geological explorations have 

 shown, that immense districts in various parts of the 

 world, have no relations in the character of their sur- 

 face, to the geological features of the region; the 

 rocks which would ordinarily show themselves upon 

 the surface, are covered, to a greater or less extent, 

 by transported materials from some other source. Such 

 observations as these, have led to the study of what 

 are called the phenomena of drift. 



The vast quantities of transported materials, which 

 thus overlie original rocks, consist, on inspection, 

 of the ruins of other formations that have been 

 broken and crumbled down, and their fragments borne 

 to other regions by some unknown power. It is clear, 

 however, that water has been one chief agent in this 

 action; for in nearly every case the stones which occur 

 in drift, are water-worn and rounded; thus showing 

 that they have been rolled along in some mighty cur- 

 rent, till all their angles have w r orn away. We s*>e 



