﻿liv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



instance of the igneous origin of basalt, where a mass of it, in some 

 places 500 feet thick, covers beds of lignite from 20 to 98 feet in 

 thickness, he says that the phenomena exhibited are to be ascribed 

 " plutot a une action aqueuse qu'a, une action ignee." Wot only in 

 the above, but in other instances, he maintains the aqueous plasticity 

 of trappean rocks. Water may be one of their constituents ; but it 

 is in no degree probable that it held the earthy constituents in a 

 softened, plastic, or fluid condition. It will require stronger proofs 

 than M. Delesse has as yet brought forward, to set aside the long- 

 established conviction of the similarity of origin of the Giant's 

 Causeway and FingaPs Cave to that of the columnar lavas of Etna 

 and Auvergne. 



Although M. Daubree does not carry his views of aqueous action 

 so far as M. Delesse does, he nevertheless expresses very decided 

 opinions as to the powerful agency of water in metamorphism, as the 

 following passage will show : — 



" It is, therefore, not difficult to see, in the various kinds of phe- 

 nomena of which I have spoken, the manifestations of one and the 

 same agent, which exists throughout entire countries. That essential 

 agent is water, aided by heat of different degrees, and to which are 

 superadded as secondary causes, emanations which accompany it. 

 Thus we are of opinion that water acts unceasingly in the deep- 

 seated regions, after it has acquired a temperature more or less 

 elevated, under the influence of the heat of the globe." — " It cannot 

 be denied that if water is able to insinuate itself, through fissures in 

 the solid crust of the globe, to a depth equal only to that of the sea, 

 it becomes subject there to a pressure equal to several hundreds of 

 atmospheres, by means of which it will penetrate easily to the inmost 

 pores of the rocks, especially when it is of a temperature which it 

 must possess at such a depth." (pp. 97 <fc 117.) 



On this agency of water the following testimony of Prof. Bunsen 

 of Heidelberg is important : — " The attention of geologists has 

 hitherto been almost solely directed to the action of heat in the 

 production of the metamorphism of rocks. The action of gases and of 

 water at a moderate temperature in producing changes of structure, 

 which may be seen on a small scale in fumaroles, must have had 

 immense influence, as after-effects of older plutonic catastrophes, 

 upon the materials of which the stratified rocks are composed. In 

 this treatise I have endeavoured to bring forward some proofs and 

 circumstances which may perhaps set geologists upon the track of 

 those processes. Everything indicates that, in future, we must rely 

 not so exclusively on observation, but more upon experimental 

 researches to enable us to explain the metamorphism of rocks by 

 hydatothermic and pyrocaustic, or, where both have acted, by 

 hydatocaustic processes. I know not whether the time is yet arrived 

 for the introduction of those terms ; but distinctions will be devoid 

 of meaning unless the test of experiment has determined their true 

 value, in every point of view*." 



* Bunsen. iiber den innern Zusammenhang der pseudo-vulianische Erschei- 

 nnngen Islands. 



