ADDRESS. Ixix 



from tlic subterranean molten mass that heat which clouds of vapour are 

 seen to carry off in a latent form from a volcanic crater during an eruption, 

 or from a lava-stream dimng its solidification. It is more than forty years 

 since Mr. Scrope, in his work on volcanos, insisted on the important part 

 whicli water plays in an eruption, when intimately mixed up with the com- 

 ponent materials of lava, aiding, as he supposed, in giving mobility to the 

 more solid materials of the fluid mass. But when advocating this igneo- 

 aqueous theory, ho never dreamt of impugning the Huttonian doctrine as to 

 the intensity of heat which the production of the unstratified rocks, those 

 of the plutonic class especially, implies. 



The exact nature of the chemical changes which hydrothcrmal action may 

 effect in the earth's interior will long remain obscure to us, because the 

 regions where they take place are inaccessible to man ; but the manner in 

 which volcanos have shifted their position throughout a vast series of geolo- 

 gical epochs — becoming extinct in one region and breaking out in another — 

 may, perhaps, explain the increase of heat as we descend towards the interior, 

 without the necessity of our appealing to an original central heat or the 

 igneous fluidity of the earth's nucleus. 



I hinted, at the beginning of this Address, that the hot springs of Bath 

 may be of no high antiquity, geologically speaking, — not that I can establish 

 this opinion by any positive proofs, but I infer it from the mighty changes 

 which this region has undergone since tlie time when the British seas, 

 rivers, and lakes were inhabited by the existing species of Testacea. It is 

 already more than a quarter of a century since Sir Eoderick Murchison 

 first spoke of the Malvern Straits, meaning thereby a channel of the sea 

 which once separated Wales from England. That such marine straits really 

 extended, at a modern period, between what are now the estuaries of the 

 Severn and the Dee has been lately confirmed in a satisfactory manner by 

 the discovery of marine shells of recent species in drift covering the water- 

 shed which di%'ides those estuaries. At the time when these shells were 

 living, the Cotswold Hills, at the foot of which this city is built, formed one 

 of the numerous islands of an archipelago into which England, Ireland, 

 and Scotland were then divided. The amount of vertical movement which 

 would be necessary to restore such a state of the surface as prevailed when 

 the position of land and sea were so different would be very great. 



Nowhere in the world, according to oiu- present information, is the 

 evidence of upheaval, as manifested by upraised marine shells, so striking as 

 in "Wales. In that country ilr. Trimmer first pointed out, in 1831, the 

 occurrence of fossil shells in stratified drift, at the top of a hill called Moel 

 Tryfacn, near the Menai Straits, and not far from the base of Snowdon. 

 I visited the spot last year, in company with my friend Mr. Symonds, and we 

 collected there not a few of the marine Testacea. Mr. Darbishire has obtained 

 from the same drift no less than fiftj'-four fossil species, all of them now 

 living either in high northern or British seas, and eleven of them being 

 exclusively arctic. The whole fauna bears testimony to a climate colder 

 than that now experienced in these latitudes, though not to such extreme 

 cold as that implied by the fauna of some of the glacial drift of Scotland. 

 The shells alluded to were procm-ed at the extraordinary licight of 1360 feet 

 above the sea-level, and they demonstrate an upheaval of the bed of the sea 

 to that amount in the time of the living Testacea. A considerable part of 

 what is called the glacial epoch had already elapsed before the shelly strata 

 in question were deposited on Moel Tryfaen, as we may infer from the 

 polished and striated siu-faces of rocks on which the drift rests, and the occur- 



