DISLOCATIONS OF STRATA. 9,5 



as unfounded in fact, as it is bottomed on an igno- 

 rance of geological phenomena. 



Jf we were to assume, in the simple case of a ver- 

 tical stratum, that it had been formed in this position, 

 we have no reason for denying, that for aught we 

 can prove to the contrary, it may reach to the centre 

 of the globe, thus rendering our knowledge of the 

 deepest regions as perfect as that of the surface. If, 

 on the contrary, we suppose that such a stratum has 

 once been horizontal, and has become vertical from 

 elevation, we have only to measure the superficial 

 extent of any large similar stratum or series of strata 

 which has been observed, and, by placing it in the 

 same position, w r e can infer the probable depth below 

 the surface, from that which is visible above it. 



But to proceed more accurately, let us suppose a 

 great horizontal tract where the edges of strata are 

 exposed. If we measure these at right angles to the 

 plane of stratification, and then suppose them restored 

 to their original horizontal position, we have dis- 

 covered the structure of the earth to at least the same 

 depth. 



This is not an imaginary case, though put in an 

 imaginary form; since examples of it occur all over 

 the world. The erected edges of a series of strata 

 are often seen following each other over large hori- 

 zontal spaces; they are often found in the acuter 

 rocky declivities of mountains, or in vertical cliffs. 

 By a simple trigonometrical operation, it is easy to 

 compute the thickness of a series ; or it might be 

 measured by a repeated addition of the dimensions 

 of the integrant strata. That thickness is the measure 

 of the original depth before elevation. Thus also it 

 may be computed to what depth from the surface, at 

 any given spot, it would be necessary to sink before 



