Ixxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Spain ; they consist mostly of sandstones and quartzites, with some 

 schists. Where the Upper Silurian formation occurs, the Devonian 

 beds rest on it ; elsewhere they lie immediately on the Lower Silu- 

 rians. It appears from the organic remains, which are very abundant, 

 that the beds belong for the most part to the Khenane, or lowest 

 division of the Devonian series ; but the middle division occurs in 

 some localities, and a few of the fossils indicate Upper Devonian beds 

 also. The species found in Spain are, in great degree, those which 

 are found in the Devonian beds wherever they occur, both in Europe 

 and North America, and lead us to the conclusion that this forma- 

 tion was deposited in an extensive and continuous ocean — or, rather, 

 I may venture to add to Mr. Sharpe's reasoning, on the shores of 

 oceans subject to the same climatal and physical conditions. No 

 vegetable remains have been found. 



Carboniferous series. — The memoir of M. Casiano de Prado does 

 not extend to this formation ; but in the palaeontological appendix 

 some localities are noticed where large calcareous deposits, hitherto 

 but slightly examined, contain Producti of this age. 



Plutonic rocks are of frequent occurrence in the region described, 

 but they offer no points of peculiar interest ; they consist principally 

 of granite and various forms of porphyry. 



The whole region described has been subjected to so much dis- 

 turbance, that the palaeozoic rocks are for the most part in nearly 

 vertical positions, and are nowhere found horizontal : a circumstance 

 which renders the determination of the relative age of the beds a 

 matter of great difficulty ; and, but for the fossils contained in them, 

 it would often be impossible to classify them. These difficulties are 

 much increased by the want of even a tolerably accurate map of the 

 country. 



M. Casiano de Prado concludes his memoir with some very inter- 

 esting remarks on the deposits of quicksilver : these are very rarely 

 found in veins, but the quicksilver, mostly in tl 3 form of cinnabar 

 (sulphuret of mercury), enters into the composition of the beds of 

 quartzite, so that after it has been roasted off, the rock remains 

 scoriaceous and so full of pores, that it frequently falls to pieces. 

 In the richest mines the quartzites in which the cinnabar occurs are 

 of the Silurian age ; but at some less important spots they are Devo- 

 nian. The slate-rocks rarely contain any mercury, and never in 

 large quantities. The plutonic rocks do not appear to have had 

 any influence on the presence or absence of the mercury ; but in this 

 respect I may add, that the sulphuret of mercury does not differ 

 from other sulphurets, and further, that it cannot be absolutely in- 

 ferred, from the apparent want of connexion of cause and effect in 

 this and similar cases, that no igneous causes have really been in 

 action in bringing the sulphur and the metal within the sphere of 

 chemical affinity. 



The first purely geological paper of the session was that of Pro- 

 fessor Harkness on the Lowest Sedimentary Rocks of the South of 

 Scotland. His first object was to trace out the axis of the Silurians 



