C 21 ] 



VII. Report of a Lecture on the Chemistry of Geology, delivered 

 at one of the Evening Meetings at the University of London* ^ 

 by Edward Turner, M.D. F.R.S. L. $ E. 9 Sec. G.S.f 



HPHE lecturer began by explaining that under the title 

 •*■ " Chemistry of Geology," he included all those geological 

 phaenomena to the elucidation of which chemical principles 

 were applicable. The subject, he said, was one of great ex- 

 tent. He might proceed to consider the affinities which ope- 

 rated in forming the crystalline rocks of the non-fossiliferous 

 series, — to develope the several theories by which it is at- 

 tempted to account for volcanic action, — to show by what 

 means the soft materials of aqueous deposites were converted 

 into solid rocks, — to trace the effects of heat in modifying the 

 appearance and nature of previously consolidated masses, — to 

 endeavour to explain the origin of mineral waters, — and spe- 

 culate on the obscure subject of the formation of veins. But he 

 would not then venture to discuss any of those topics, the rather 

 as some of them were then under investigation. He meant 

 to confine his remarks to two parts of the subject : First, to 

 the causes which give rise to the degradation of rocks, thereby 

 providing the materials for new by the destruction of pre- 

 existing geological formations ; and, secondly, to the produc- 

 tion, by means of aqueous solution, of siliceous and other de- 

 posites which were commonly regarded as insoluble. He 

 would touch cursorily on the former, chiefly with a view to 

 facilitate the comprehension of the latter. 



I. Disintegration of Rocks. — The principal agents con- 

 cerned in the degradation of rocks might, it was said, be con- 

 veniently arranged under three heads : — 



1. Mechanical agents; such as rain, rivers, and torrents, or, 

 generally, water in motion. — This subject, the lecturer said, 

 did not require comment on that occasion, as it was not only 

 familiar to geologists, but foreign to the plan of his lecture. 



2. The alternate congelation and liquefaction of water. — In 

 all situations liable to alternate frost and thaw, this was a most 

 fertile source of destruction to rocks. 



Water, insinuating itself into fissures or between the strata 

 of rocks, and congealing there, tore asunder the firmest masses 

 by the immensely expansive force which water exerts in freez- 

 ing, kept together the disjointed parts, as by cement, while it 



* See Lond. and Edinb. Phil. Mag. for June, page 479. 



f The interest as well as the length of this report have induced us to 

 prefer giving it its present place, to inserting it in our " Proceedings of 

 Learned Societies." — Edit. 



