Geological Society. 461 



extensive to form an adequate base for his deductions ; but there 

 can be no question as to many of his inferences, nor respecting the 

 impulse which the subject will receive from such an accumulation 

 of facts as he has brought together. His views contrasting the 

 climate of the globe at former periods and at the present time, — 

 and his division of the epochs of geological deposition, as deduced 

 from the study of fossil plant';, in comparison with those which mere 

 geological inquiry points out, — are most ingenious. Even if re- 

 garded as no more than the conjectures of so acute and indefa- 

 tigable an inquirer, these speculations would be well deserving of 

 attention ; and altogether, his works on Fossil Plants must be con- 

 sidered as constituting one of the most valuable conti'ibutions to 

 this department of Geology that has ever appeared. 



We have received from our foreign members Messrs. Oeynhausen 

 and Dechen, a paper on Ben-Nevis, the highest mountain in Scot- 

 land, which gives rise to some general reflections of great interest 

 to theory :— And I mention this contribution with the greater plea- 

 sure, because I know that it is a peculiar gratification to the Society 

 to receive the papers of foreigners; and that if, in any instance, our 

 aid, either as a Society or individually, has promoted the inquiries 

 of travellers in England, they may be assured that no return can 

 be more acceptable to us, than the illustration of our own country 

 by their publications, or the application of the knowledge which 

 they have acquired here, to elucidate the corresponding tracts of 

 the Continent. 



The summit of Ben-Nevis consists of porphyry ; the flanks are 

 granite, on which again is incumbent mica-slate. Messrs Oeyn- 

 hausen and Dechen have ascertained that the porphyry, instead of 

 being an overlying mass, as has been asserted in similar cases, 

 comes up through the granite; and that, as veins shooting from 

 the granite are found to penetrate the incumbent mica-slate, so 

 veins of the porphyry shoot into the granite itself, and thus de- 

 monstrate the more recent protrusion of the former compound. 

 It has long been known, that granite, in the Isle of Arran and at 

 Newry in Ireland, is traversed by veins of pitchstone, which itself 

 is only a variety of porphyry : and Mr. Knox's detection of bitumen 

 in pitchstone of every age, as well in various other rocks of the 

 trap formation*, coincides with this evidence, in demonstrating the 

 igneous origin of that entire series of compounds. The light which 

 the observations of Messrs. Oeynhausen and Dechen throw upon 

 the " Elvans," or porphyritic veins of Cornwall, was alluded to in 

 the conversation which followed the reading of their paper here ; 

 for these Elvans are in fact great veins of porphyry : and since it 

 would be inconsistent and unphilosophical to assign the production 

 of phacnomena of the same ciiaracter to dift'ercnt causes, the pro- 

 bable origin of ail veins, cither by injection or sublimation from 

 below, receives from these facts new and independent supportf . 



• Phil. Trans.; 1S22 and 182.'}. 



t Messrs. Ocynliauscn :iml Dcchcn's paper on the piixnonicna of veins, 

 itc. altcniliii): tlic jniu'tion of the ■,'riinito aixl tiie kilhis in Coriiwall, will be 

 found at p. 1/0 and i.'ll of the |)reseiil voliiiiie, — Kuri. 



The 



