105 



not be found under No. 2, nor any other in the inverted order. 

 A deposit may be of the same age and belonging to the same 

 zone, that is, exactly equivalent to another, and yet differ both 

 in lithological and zoological character, and thus cannot be deter- 

 mined without the aid of the inferior and superior beds. 



During a late survey in Ireland the writer saw pits being sunk 

 in No. 1 in search of No. 2 (coal) on the eastern side of the 

 Wicklow mountains ; although no fossil could be detected in No. 

 1 to prove that coal could not exist below, yet the structure of 

 the beds, and their lamination, enclosing veins of quartz and 

 pyrites, were sufficient to show, not only their contact with the 

 primary base, but their actual transition : it was like cutting 

 into the body of a tree in search of the bark. When the upper 

 series of the sedimentary beds are much developed the lower are 

 seldom found underneath, and vice versa ; it is essential to bear 

 this fact in mind when making trials for coal below the Chalk, 

 Oolite, &c, as a thick seam of coal could not exist, even had it 

 been originally deposited in the spot, under such a pressure as 

 would be produced by a complete set of the superincumbent 

 series ; therefore those who have studied geology from theoretical 

 sections must modify their ideas on this point. 



It is a very common observation in geological works, " that 

 we can, by the aid of geology, see as it were into the interior 

 thirty miles or more ; for Pallas had described, in the peninsula 

 of Tauris, a series of parallel strata as regular as the leaves of a 

 book, inclined at an angle of 45° to the horizon, and exposed in 

 a continuous section eighty-six English miles long/' The above 

 series is a laminated crystalline rock, and not sedimentary beds. 

 In South America, we may see sections of such a series for up- 

 wards of 300 miles in extent, in an east and west direction, 

 exhibiting such inclined planes. To deduce the thickness of 

 the earth's crust by the planes of lamination, is like calculating 

 the depth of a transverse section of a tree by the medullary rays 

 instead of the concentric rings. 



The more recent deposits must necessarily be less contorted 

 and fractured as a whole than those which are more ancient, on 

 account of their being subject to less disturbances, and not so 

 compact : the fractures and dislocations visible on the surface of 

 any series of rocks would not afford a just estimate of the amount 



