144 



ALTERNATING BEDS OF LAVA, ETC. 



wacke, which is much intermixed with green earth, and has in some 

 parts a saponaceous feel ; the agates which it contains are decompo- 

 sing, and the inner concentric layers are separated from each other, 

 and present the appearance of edges of folded paper, with small in- 

 terstices between each. I examined this singular rock in 1816; it 

 was then quarried for stone to mend the roads. In some parts of 

 the rocks, I found masses of corallite of considerable size, enveloped 

 in the basaltic amygdaloid. I found also, in this rock, well defined 

 groups of prehnite, which was not then known to be an English min- 

 eral : it has since been discovered in the basalt of Staffordshire. 



The occurrence of organic remains enveloped in basalt, of which 

 there are various instances, may admit of an easy explanation, if we 

 allow that basalt has once flowed like lava at the bottom of the ocean. 

 Modern lavas often envelope bones and other substances that they 

 meet with in their course. 



Having before stated the phenomena presented by imbedded trap, 

 which indicate that, in some instances, it has been protruded between 

 regular strata laterally, it will be useful to cite an instructive exam- 

 ple of beds of trap alternating with limestone, by successive deposi- 

 tion, which is stated by Dr. Daubeny, the present chemical professor 

 at Oxford, in an interesting sketch of the Geology of Sicily. The 

 facts seem clearly to ascertain, that beds of amygdaloidal trap, aher- 

 nating with beds of limestone, have, in that island at least, been 

 formed by successive currents of lava flowing over the bed of the 

 sea, at intervals of time so distant, as to allow the deposition or for- 

 mation of a bed of limestone, over each current of lava. A consid- 

 erable district near Lentini, on the southern side of Mount Etna, and 

 also a part of the island near Cape Passero, are composed of alter- 

 nating beds of lava, with tertiary limestone abounding with organic 

 remains of madreporites, nummulites, cerithea, and the remarkable 

 fossil called the Hippurite. Santa Venera, the loftiest mountain in 

 the south of the island, is capped with cellular lava ; beneath it is a 

 bed of limestone with minute shells ; at a lower level, towards Len- 

 tini, there is a second bed of volcanic matter similar to the first; and 

 two other similar alternations of beds of limestone and lava occur 

 still lower down. Dr. Daubeny says that the cellular and semi- 

 vitreous aspect of many of the volcanic beds associated with the beds 

 of limestone, precludes all doubt respecting the manner of their 

 formation : the character of other portions presents strong analogies 

 to rocks of the trap family ; they are compact, and have a stony 

 fracture ; they contain crystals of olivine, and the cavities are filled 

 with calcareous spar or zeolites, like the amygdaloids of more an- 

 cient strata. In some of the beds, a tendency to a columnar ar- 

 rangement is discernible." 



This account of Dr. Daubeny's, affords additional proof of the 

 close connection of ancient volcanic rocks with trap rocks, — may 

 we not add, of their perfect identity ? It is beside highly illustrative 



