Ch. XXXIV.] PLUTONIC ROCKS OF OOLITE AND LIAS. 579 



have occurred in the earth's crust within an equal quantity of time an- 

 terior 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 hjpogene 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 hypogene rocks. In 

 the course of such changes many of the existing sedimentary strata 

 would suffer greatly by denudation, others might assume a meta- 

 morphic 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 partial 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 shown 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 decided. 

 Kg. 698. Suppose b, c, d, to be three members of 



the Cretaceous series, the lowest of which, 

 b, has been altered by the granite A, the 

 modifying influence 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 

 I 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. 



Period of Oolite and Lias. — In the department of the Hautes Alpes, 

 in France, near Vizille, M. Elie de Beaumont traced a black argillaceous 

 limestone, charged with belemnites, to within a few yards of a mass of 

 granite. Here the limestone begins to put on a granular texture, but 

 is extremely fine-grained. When nearer the junction it becomes gray, 

 and has a saccharoid structure. In another locality, near Champoleon, a 

 granite composed of quartz, black mica, and rose-colored felspar, is 

 observed partly to overlie the secondaty rocks, producing an alteration 

 which extends for about 30 feet downwards, diminishing in the beds 

 which lie farthest from the granite. (See fig. 699.) In the altered 





