Geological Society of London. 281 



of the Old Bed Sandstone on the south of the South- Wales Coal-field. 

 This was found to be a little over 4000 feet. The thinning out of 

 the Old Red Sandstone and Silurian, strata, together with the marked 

 change which takes place correspondingly in the lithological cha- 

 racters of the latter formation on passing from the north to the 

 south side of the coal-field were taken to indicate an approach to a 

 shore-line. This shore-line belonged to land which, as shown by 

 the great thickness of the Devonian beds, could not have extended 

 far south. It corresponded to Mr. Etheridge's barrier between the 

 Old Red Sandstone and Devonian seas. The sandstones with Old-Red 

 characters, such as the Hangman G-rit and the Pickwell-Down 

 Sandstones, occurring in the Devonian formation, were deposited at 

 intervals when this barrier was submerged to a greater depth than 

 usual. The Cornstones were stated to thin out to the south along 

 with the other sedimentary beds of the Old Red Sandstone, and 

 were regarded as derived from the denudation of previously up- 

 heaved limestones, such as the Bala and Hirnant. The paper con- 

 cluded with a description of the characters of the more interesting 

 rocks and fossils. 



II— April 30, 1879.— Henry Clifton Sorby, Esq., F.R.S., President, 

 in the Chair. — The following communications were read : — 



1. " A Contribution to the History of Mineral Veins." By John 

 Arthur Phillips, Esq., P.G.S. 



In this paper the author described the phenomena of the deposition 

 of minerals from the water and steam of hot springs, as illustrated 

 in the Californian region, referring especially to a great " sulphur 

 bank " in Lake County, to the steamboat springs in the State of 

 Nevada, and to the great Comstock lode. He noticed the formation 

 of deposits of silica, both amorphous and crystalline, inclosing other 

 minerals, especially cinnabar and gold, and in some cases forming 

 true mineral veins. The crystalline silica formed contains liquid- 

 cavities, and exhibits the usual characteristics of ordinary quartz. In 

 the great Comstock lode, which is worked for gold and silver, the 

 mines have now reached a considerable depth, some as much as 2660 

 feet. The water in these mines was always at a rather high tem- 

 perature, but now in the deepest mines it issues at a temperature of 

 157° Fahr. It is estimated that at least 4,200,000 tons of water are 

 now annually pumped from the workings ; and the author discussed 

 the probable source of this heat, which he was inclined to regard as 

 a last trace of volcanic activity. 



2. ''■ Vectisaurus valclensis, a New Wealden Dinosaur." By J. W. 

 Hulke, Esq., F.R.S., F.G.S. 



The author described some fossil remains, obtained by him in 

 Brixton Bay, Isle of Wight, in 1871, consisting of an ilium, several 

 pre-sacral, and one post-sacral vertebra. He established the Dino- 

 saurian nature of the animal represented by them, and offered proof 

 of its distinctness from already-known forms. He proposes for it 

 the name Vectisaurus valdensis, a name descriptive of the locality and 

 formation in which the remains were found by him. The characters 



