6 Principles of Geology. 



rocks is confined to no country ; for whether in the new or the old 

 world, in conlinenls or in islands, it is so remarkable and so constant, 

 that colliers sink deep pits, and miners undertake expensive levels, 

 in full confidence that no exception to its generality will affect the 

 success of their enterprises. It is not a speculative truth, but a prac- 

 tical law of nature, and is, probably, the fact of most extensive in- 

 fluence in the whole system of geology. 



The Wernerian school of geology held it to be a universal law, of 

 structure, and even Cuvier says, " All rocks are stratified." But 

 such expressions are incorrect. How can the term strata be applied 

 to basalt, porphyry, and other unconformed masses? That granite is 

 sometimes internally stratified, has been asserted, — an appearance I 

 never witnessed, — but every geologist knows abundance of exam- 

 ples in which it displays no trace of such a structure. These rocks, 

 and some few others, are exceptions to the law of stratification; and 

 if, as appears probable, their origin is different from that of stratified 

 rocks, we need not wonder that they assume other modes of arrange- 

 ment. But, neglecting these particular rocks, it is certain that strat- 

 ification is the most general phenomenon hitherto discovered by geol- 

 ogists. Recognised by observers of different opinions, and in op- 

 posite quarters of the globe, it well deserves to be considered a fun- 

 damental doctrine. Let us inquire how these strata are combined 

 in the crust of the earth ; for so, perhaps, we may best designate the 

 very limited depth to which it has been explored by human enter- 

 prise and science. 



To ascertain the manner in which strata are placed in the crust of 

 our globe, is certainly the great object of practical geology. The 

 first rudiments of this knowledge should be early implanted in the 

 mind of the student, by leading him to the contemplation of some 

 well-marked natural section. Let him visit the sea-coast, and ob- 

 serve for himself whether or not the following proposition is true. 



That, in a local tract, strata are superimposed on one another in a 

 certain constant order of succession, like the leaves of a book. 



Let us take the Yorkshire coast for an example. Gristhorpe cliff 

 is crowned by calcareous sandstone rocks, which lie upon a thick ar- 

 gillaceous stratum ; under this is a brown ferruginous rock ; and still 

 lower is a thin calcareous layer full of fossils. The same calcareous 

 sandstone is found on the top of Red cliff, and it rests in the same 

 manner upon the argillaceous stratum, brown rock, and fossil bed. 

 In Scarborough castle hill, the same calcareous sandstone, argillace- 



