Geological Society : — Anniversary of 1839. 237 



Dynamics, in a paper in which he ascribed the earthquakes which 

 took place in the southern provinces of Spain, in 1829, to the 

 falling in of strata, the subjacent gypseous and saliferous masses 

 being washed out by subterraneous currents.* Without denying 

 all influence to such a cause, we may observe that it does not 

 appear likely that there would be thus produced, simultaneously, 

 any greater effects than those which are known to have occurred 

 from the falling in of unsupported mines ; and these have never 

 approached in their scale to any except the smallest earthquakes. 

 While geologists are thus looking in all directions for causes 

 which may produce the phenomena which they study, it is natu- 

 ral that the powerful, but as yet mysterious influences of elec- 

 tricity should draw their attention. Mr. Robert Were Fox has 

 endeavored to show, that by voltaic agency, a laminated struc- 

 ture, and deposits of metal in cracks, resembling metallic veins, 

 may be produced in masses of clay. The experiments are of an 

 interesting kind, and it can hardly be doubted that voltaic agency 

 had some influence in such cases as those described by Mr. Fox ; 

 although Mr. Henwood and Mr. Sturgeon have failed in attempt- 

 ing to reproduce his results, and although results much resem- 

 bling these occur in cases where no electrical action is suspected. 

 But we may remark that the conditions under which such voltaic 

 effects are produced have not yet been attempted to be defined 

 with any accuracy ; and that till this is done, the reality of such 

 agency can neither be verified nor applied to geological specula- 

 tions. 



A reflection which naturally offers itself upon this review of 

 our recent career, is this : — that different portions of the science of 

 geology advance with very different rapidity. Descriptive Geol- 

 ogy is constantly and actively progressive : facts are accumulated 

 by observers in every land ; and though facts are, in truth, of no 

 value, at least for any purpose of science, except so far as they 

 are reduced to some classification, yet on the other hand, sound 

 classifications are perpetually, almost necessarily, suggested, when 

 observation is vigilant and persevering. Even if we at first ex- 

 press our facts in terms of a false classification, we find afterwards 



[* An abstract of M. Necker's paper has appeared in the present volume, p. 

 370.— El.. Lon. and Ed. Phil. Mag. 



