1 70 Geological Society. 



connexion with the phenomena of drift) to absolute proof, of the 

 close relation of the acts of upheaval and violent aqueous abrasion. 

 This necessarily implies the belief that the date of these lines of 

 disturbance is posterior to that of all the stratified beds of the south- 

 east part of England, as maintained in the author's former essays, 

 but into the full discussion of which he declines to enter till tbe 

 whole subject is before the Society. 



Jan. 6, 1S41. — A paper was first read " On the Illustration of 

 Geological Phsenomena by means of Models," by Thomas Sopwith, 

 Esq.,F.G.S. 



Mr. Sopwith commences by stating, that drawings cannot con- 

 vey to the mind a correct notion of geological phamomena where 

 more planes than one are required ; and that few persons are aware 

 of the extraordinary changes which are produced in the combina r 

 tions of strata by viewing them on different planes, especially if the 

 strata are dislocated ; or in undisturbed and parallel strata, of the 

 totally different apparent forms which are exhibited on an un- 

 dulating surface and in any plane section of the interior. This 

 difference is of great importance in mining plans, where the sur- 

 face only in the first instance is accessible to examination, and the 

 observer is too apt to infer from it, the subterranean relations of 

 the strata. To convey clear notions of these differences Mr. Sop- 

 with has prepared a series of hand models, about two inches square, 

 formed of layers of differently coloured woods, and capable of being 

 dissected, to a certain extent, vertically, obliquely or horizontally. 

 They are also so shaped on the upper surface as to exhibit the un- 

 dulations of the ground. It is not possible to convey verbally, a 

 clear notion of the many curious combinations exhibited by these 

 models. 



A paper was next read, " On the Geology of the island of Ma- 

 deira," by James Smith, Esq., of Jordan Hill, F.G.S. 



The crust of that island, Mr. Smith states, is composed to the 

 depth of several thousand feet of subaerial volcanic matter, erupted 

 during the tertiary period ; and he adds, perhaps no other volcanic 

 region offers more favourable opportunities for investigation. To 

 account for its rugged and fragmentary character, it is not neces- 

 sary, he says, to have recourse to the supposition that Madeira 

 is one of the remains of a vast continent, as there are in the vol- 

 canic constitution of the island, and in the action of the mountain 

 torrents, sufficient elements to afford data for explaining every 

 physical phenomenon. 



The igneous rocks composing the greater part of the island, are 

 lavas, sand, and ashes, with bombs, lapilli, pumice, volcanic scoriae or 

 cinders, tufas and conglomerates ; and the non-igneous, the limestone 

 of San Vincente, the coal or lignite of San George, and the sands 

 of Canical. 



Volcanic Rocks. 



The lavas are wholly basaltic, containing numerous crystals of 

 olivine ; and they are compact, scoriaceous and vesicular. 



The compact variety occurs in beds or coulees interstratified with 



