6 PRINCIPLES OF GEOLOGY. 



porphyry, and other unconformed masses ? That granite is sometimes 

 internally stratified, has been asserted, an appearance I never wit- 

 nessed, but every geologist knows abundance of examples 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 pro- 

 bable, their origin is different from that of stratified rocks, we need not 

 wonder that they assume other modes of arrangement. But, neglecting 

 these particular rocks, it is certain that stratification is the most general 

 phenomenon hitherto discovered by geologists. Recognised by observers 

 of different opinions, and in opposite quarters of the globe, it well 

 deserves to be considered a fundamental 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 enterprise 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 rudi- 

 ments 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 observe 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. (See the Section.) 

 Gristhorpe cliff is crowned by calcareous sandstone rocks, which lie upon 

 a thick argillaceous stratum ; under this is a brown ferruginous rock ; 

 and still lower is a thin calcareous layer full of fossils. The same cal- 

 careous 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, argillaceous 

 stratum, brown rock, and fossil bed, occur in the very same order of 

 succession. It is needless to multiply examples, or every part of the 

 coast from Flamborough to Saltburn might be cited in proof of the 



