696 CRETACEOUS VOLCANIC ROCKS. [Oh. XXXII. 



Ganoids, which form, as before stated, the vast majority of the ich- 

 thyolites entombed in the secondary rocks. 



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. Yirlet, 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 ex- 

 ample, which alternate conformably with cretaceous limestone and 

 greensand between Kastri and Darnala 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 

 established by the following proofs : first, the lithographic limestones 

 of the Cretaceous era are cut through by trap, and then a conglomer- 

 ate occurs, at Naupila and other places, containing in its calcareous 

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

 with pebbles 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 during the Oolitic period ; * and it is probable 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. 



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

 country, originated contemporaneously with the Oolite which they 

 traverse and overlie, has been ascertained by Professor E. Forbes, in 

 F850. 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 Sandstone Period. — In the southern part of 

 Devonshire, trappean rocks are associated with New Keel Sandstone, 

 and, according to Sir H. de la Beche, have not been intruded subse- 

 quently 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 conglom- 

 erates occurring near Tiverton are many angular fragments of trap 

 porphyry, some of them one or two tons in weight, intermingled with 

 pebbles of other rocks. These angular fragments were probably 

 thrown out from volcanic vents, and fell upon sedimentary matter 

 then in the course of deposition.! 



Carboniferous Period. — Two classes of contemporaneous trap rocks 

 were ascertained by Dr. Fleming to occur in the coal-field of the 



* Boblaye and Virlet, Morea, p. 23. 



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



% De la Beche, Geol. Proceedings, vol. ii. p. 198. 



