Ch. xxxil] cretaceous volcanic rooks. 555 



and limestones in the upper part of that hill were introduced, like tlie 

 dike, subsequently, by intrusion from below. They must have been 

 thrown down like sediment from water, and can only have resulted from 

 igneous action, which was going on contemporaneously with the deposi- 

 tion of the lacustrine strata. 



The reader will bear in mind that this conclusion agrees well with the 

 proofs, adverted to in the fifteenth chapter, of the abundance of silex, 

 travertin, and gypsum precipitated when the upper lacustrine strata were 

 formed ; for these rocks are such as the waters of mineral and thermal 

 springs might generate. 



Cretaceous period. — Although we have no proof of volcanic rocks 

 erupted in England during the deposition of the chalk and greensand, it 

 would be an error to suppose that no theatres of igneous action existed 

 in the cretaceous period. M. Virlet, in his account of the geology of 

 the Morea, p. 205, has clearly shown that certain traps in Greece, called 

 by him ophiolites, are of this date ; as those, for example, which alter- 

 nate conformably with cretaceous limestone and greensand between Kas- 

 tri and Damala in the Morea. They consist in great part of diallage 

 rocks and serpentine, and of an amygdaloid with calcareous kernels, and 

 a base of serpentine. 



In certain parts of the Morea, the age of these volcanic rocks is es- 

 tablished by the following proofs ; first, the lithographic limestones of 

 the Cretaceous era are cut through by trap, and then a conglomerate 

 occurs, at Nauplia and other places, containing in its calcareous cement 

 many well-known fossils of the chalk and greensand, together with peb- 

 bles formed of rolled pieces of the same ophiolite, which appear in the 

 dikes above alluded to. 



Period of Oolite and Lias. — Although the green and serpentinous 

 trap rocks of the Morea belong chiefly to the Cretaceous era, as before 

 mentioned, yet it seems that some eruptions of similar rocks began dur- 

 ing the Oolitic period;*' and it is probable, that a large part of the 

 trappean masses, called ophiohtes in the x\pennines, and associated with 

 the limestone of that chain, are of corresponding age. 



That some part of the volcanic rocks of the Hebrides, in our own coun- 

 try, originated contemporaneously with the Oolite which they traverse and 

 overlie, has been ascertained by Prof. E. Forbes, in 1850. Some of the 

 eruptions in Skye, for example, occurred at the close of the Middle and 

 before the commencement of the Upper Oolitic Period.f 



Trap of the New Red Sai^dstone 2^6^'iod. — In the southern part of 

 Devonshire, trappean rocks are associated with New Eed Sandstone, and, 

 according to Sir H. 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 many angular fragments of trap porphyry, some of them 

 * Boblaye and Virlet, Morea, p. 23. 

 f Geol. Quart. Journ. 1851, vol. vii. p. 108. 



