Ch. XII.] NATURE OF STRATIFICATION. 251 



parallel ; or it may be level above, but convex beneath, 

 owing to its having been formed in a basin-shaped hollow, or 

 any other kind of concavity ; or, on the other hand, it may 

 be a simple cuneiform mass, thick at one end and tapering 

 towards the other ; or it may be thick in the middle, gradually 

 diminishing towards both extremities, such as sand-banks 

 present when within the reflux of the waves from the shore. 

 In short, the entire mass may be of a regular form, or exhibit 

 the most irregular and uncouth appearances, according to 

 the circumstances under which it has been produced. Now 

 we find similar masses in every geological era, presenting the 

 same aspects ; and, according to the best of our judgment, 

 perfectly analogous : and such masses, when consolidated, are 

 traversed by horizontal or inclined parallel joints, the inter- 

 vening layers being often again divided by other intersecting 

 planes. Are we then justified, in this case, to attribute either 

 of these systems of joints (and why not one as well as 

 another ?) to an arrangement effected during their aqueous 

 formation? Surely it must have forcibly struck everyone 

 who has carefully considered this subject, that all these lines 

 have proceeded from some cause, operating subsequently to 

 the deposition of the mass. 



This statement does not depend altogether on the correct- 

 ness of the arguments now advanced, and some may perceive 

 objections to the analogy adduced, which have escaped our 

 notice ; it may, therefore, not be irrelevant to mention that 

 the testaceous sand-banks, on the northern shore of Cornwall, 

 furnish us with a practical illustration of this subject. Some 

 of these banks are situated above high-water mark, resting on 

 a bed of pebbles and shingle, into which they gradually pass, 

 by the intermixture of the sand with the pebbles. The upper 

 parts of these banks are homogeneous, and assume various 

 irregular external forms, yet wherever this sand has been 

 lapidified, it may be generally found consolidated into hori- 

 zontal layers, sometimes not exceeding an inch or two in 

 thickness. This occurrence in a rock so recently formed is 



