70 
PRIMITIVE ROCKS. 
fore, we see a mountain bounded by a plain, we are 
not to suppose that the strata of which it is formed 
terminates at its base, but rather that they dip 
under the other rocks at angles more or less incli- 
ned, penetrating far into the interior of the earth, 
and often rising again in remote districts.* It is 
proper, perhaps, here to remark, that Mr. Lyell, the 
distinguished President of the London Geological 
Society, in his Elements of Geology, objects to the 
word primitive^ on the ground that it is not true that 
all granites and rocks called primitive were first 
formed, and the aqueous and volcanic rocks super- 
imposed. He thinks that granite has originated at 
different epochs, some antecedent, others subse- 
quent to the origin of many fossiliferous strata, and, 
by the agency of internal heat, ejected in the form 
of veins or dikes through the superincumbent rocks, 
perhaps changing the very rock containing fossils 
into crystalline granite or gneiss. He therefore pro- 
poses the iQYm hypogene, from the Greek words sig- 
nifying " under" and " to be born," signifying that 
such rocks are formed beneath the others, and have 
not assumed their present form and structure at the 
surface. He also calls such rocks Plutonic, because 
he believes they could not have acquired their crys- 
talline structure unless they had been modified by 
the agency of heat under great pressure in the 
depths of the earth. 
De la Beche also remarks, " that in the earlier days 
of geology^ granite was considered the fundamental 
rock on which all others were accumulated ; but 
this opinion, like many others, has now given way 
before facts : for we have examples of granite rest- 
ing upon stratified and fossihferous rocks of no very 
great comparative antiquity. It must, however, be 
confessed, that granite appears sometimes to alter- 
nate in considerable thickness with the inferior strat- 
ified rocks, and that the separation of it from gneiss 
* Bakeweil's Geology. 
