Ch. XXXIV.] PLUTONIC ROCKS OF OOLITE AND LIAS. ?23 



ception of a few districts, emerged from the deep to its present alti- 

 tude ; and even those tracts which were already dry land before the 

 Eocene era, have, in many cases, acquired additional height. A large 

 amount of subsidence has also occurred during the same period, so 

 that the extent of the subterranean spaces which have either become 

 the receptacles of sunken fragments of the earth's crust, or ha^e been 

 rendered capable of supporting other fragments at a much greater 

 height than before, must be so great that they probably equal,, if not 

 exceed in volume, the entire continent of Europe. "We are entitled, 

 therefore, to ask what amount of change of equivalent importance can 

 be proved to have occurred in the earth's crust within an equal quan- 

 tity of time anterior to the Eocene epoch. They who contend for 

 the more intense energy of subterranean causes in the remoter eras 

 of the earth's history may find it more difficult to give an answer to 

 this question than they anticipated. 



The principal effect of volcanic action in the nether regions during 

 the tertiary period seems to have consisted in the upheaval to the sur- 

 face of hypogene formations of an age anterior to the carboniferous. 

 The repetition of another series of movements, of equal violence, 

 might upraise the plutonic and metamorphic rocks of many secondary 

 periods ; and, if the same force should still continue to act, the next 

 convulsions might bring up to the day the tertiary and recent hypo- 

 ( gene rocks. In the course of such changes many of the existing sedi- 

 mentary strata would suffer greatly by denudation, others might 

 assume a metamorphic structure, or become melted down into plutonic 

 and volcanic rocks. Meanwhile the deposition of a vast thickness of 

 new strata would not fail to take place during the upheaval and par- 

 tial destruction of the older rocks. But I must refer the reader to the 

 last chapter but one of this volume for a fuller explanation of these views. 



Cretaceous Period. — It will be seen in the next chapter that chalk, 

 as well as lias, has been altered by granite in the eastern Pyrenees. 

 "Whether such granite be cretaceous or tertiary cannot easily be de- 

 cided. Suppose b, c, d, fig. 750, to be 

 three members of the Cretaceous series, m %- 75 °- 



the lowest of which, b, has been altered 

 by the granite A, the modifying influ- 

 ence not having extended so far as c, or 

 having but slightly affected its lowest 

 beds. Now it can rarely be possible for 

 the geologist to decide whether the beds 



d existed at the time of the intrusion of A, and alteration of b and c, 

 or whether they were subsequently thrown down upon c. 



But as some Cretaceous and even tertiary rocks have been raised 

 to the height of more than 9000 feet in the Pyrenees, we must not 

 assume that plutonic formations of the same periods may not have 

 been brought up and exposed by denudation, at the height of 2000 

 or 3000 feet on the flanks of that chain. 



— — — d — 



