278 LYELL'S ELEMENTS OF GEOLOGY. 



Volcanic Rocks. 



tuffs were probably the product of submarine eruptions in the 

 cretaceous sea. 



The traps of this country and of the neighbouring Pyrenees 

 are generally ophitic, and many French geologists consider them 

 to be newer than the cretaceous period, and therefore tertiary ; 

 but I know of no sections which demonstrate this point. M. 

 Charpentier has argued that the ophites of the Pyrenees were 

 more modern than all the secondary strata of that chain, because 

 in the conglomerates constituting the upper part of the creta- 

 ceous series on the flanks of the Pyrenees, no rolled pebbles of 

 ophite have been found.* But this negative fact may be ex- 

 plained by supposing that, in the cretaceous sea, which occupied 

 the space where the Pyrenees now stand, the ophitic eruptions 

 were submarine, and never formed islands or shoals exposed to 

 denudation. 



The age of the trap of Antrim in Ireland, before described, as 

 altering the chalk by its dikes (p. 107.), is uncertain. It is 

 newer than the chalk of that region, which it cuts through and 

 overflows ; and perhaps it belongs to some one of the tertiary 

 periods. As wood-coal and coniferous fossil trees have been 

 found associated with it on the eastern shore of Lough Neagh, 

 these plants may hereafter throw light on this chronological 

 question, f 



Period of Oolite and Lias. Although the green and serpen- 

 tinous trap rocks of the Morea belong chiefly to the cretaceous 

 era, as before-mentioned, yet it seems that some eruptions of 

 similar rocks began during the oolitic period ;f and it is proba- 

 ble, that a large part of the trappean masses, called ophiolites in 

 the Apennines, and associated with the limestone of that chain, 

 are of corresponding age. 



Whether part of the volcanic rocks of the Hebrides, in our 

 own country, originated contemporaneously with the lias and 

 oolite which they traverse and overlie, remains to be ascer- 

 tained. 



Trap of the New Red sandstone period. In the southern 

 part of Devonshire, trappean rocks are associated with new red 

 sandstone, and, according to Mr. De la Beche, have not been 

 intruded subsequently into the sandstone, but were produced by 

 contemporaneous volcanic action. Some beds of grit, mingled 

 with ordinary red marl, resemble sands ejected from a crater; 

 and in the stratified conglomerates occurring near Tiverton are 



* Charpentier, Essai Geog. sur ies Pyrenees, p. 524. 

 t Dr. Berger, Geol. Trans. 1st series, vol. iii. p. 183. 

 t Boblaye and Virlet, Morea, p. 23. 



