220 Geological Society. 



A paper was afterwards read, " On the several Ravines, Passes,and 

 Fractures in the Mendip Hills and other adjacent Boundaries of the 

 Bristol Coal-field, and on the geological Period when they were ef- 

 fected," by the Rev. David Williams, F.G.S. 



The district included in this memoir comprehends the western 

 portion of the Mendip Hills, and the western and north-western 

 boundaries of the Bristol coal-field. It presents a series of lofty ridges 

 composed of mountain limestone and traversed by deep transverse 

 ravines which connect the valleys on the opposite sides of the ridges. 

 The author describes, in great detail, the characters, both physical 

 and geological, of each ravine j and shows that in consequence of 

 their being filled, in part, with horizontal beds of dolomitic conglo- 

 merate, red marl, and lias, they were formed previously to the 

 deposition of those formations ; but he also shows that the ravines 

 have been subsequently acted upon by a body of water, forming 

 what he terms valleys of denudation in valleys of elevation. 



In describing thedefile of St. Vincent's Rocks, near Bristol, the 

 author states, that he has discovered two lines of fracture indepen- 

 dent of the one noticed in the memoir of Dr. Buckland and Mr. 

 Conybeare on the south-western coal-field*. He says that the prin- 

 cipal evidence which he has of the existence of these two faults, 

 rests on the beds of clay, belonging to the lower limestone shale, 

 occurring twice on both sides of the ravine between the first fault 

 and the commencement of the shale beds in their true position 

 beneath the mountain limestone. 



In alluding to the bone-caves and fissures of the Mendip Hills, 

 the author conceives that they were formed contemporaneously 

 with the ravines ; and that he had found among their organic 

 contents the remains of the Mastodon. 



April 23.— A paper was first read, i( On the Tertiary Forma- 

 tions of the Kingdom of Murcia, in Spain," by Charles Silvertop, 

 Esq., retired Brigadier in the Spanish Service, K. R. O. C. III., 

 F.G.S. 



This memoir is a continuation of papers on the tertiary formations 

 of the South of Spain, read before the Society during the last and 

 preceding Sessionsf. The district described is situated in the south- 

 eastern portion of the kingdom of Murcia, and consists of extensive 

 plains and valleys of tertiary formations, bounded by discontinuous 

 ridges of mica slate, transition rocks, and nummulitic limestone. 

 The tertiary deposits the author divides into four districts, which 

 he names from the principal towns situated in their immediate 

 neighbourhood, viz. Lorca, Totana, Alhama and Mula, and Car- 

 tagena. 



The tertiary strata of Lorca he separates into two systems, one 

 characterized by the beds being horizontal, the other by their being 

 highly inclined. The horizontal beds consist of reddish friable 



* Geol. Trans., 2nd Ser., vol. i. p. 241. 



t See Phil. Mag. and Annals, N.S., vol. vii. p. 453; vol. viii. p. 150; 

 Lond. and Edinb. Phil. Mag. vol. iii. p. 370. 



