Geological Society. 227 



but tlint, on the contrary, as soon as the unstratified rocks recom- 

 mence in the last-mentioned district, metallic veins reappear. 



Lastly, the author compares the relative connexion ot igneous de- 

 posits with metallic accumulations, and states that ores are more 

 abundant in granite, certain porphyries, syenites, amygdaloids, and 

 trap, which he calls underlying, unstratified rocks, than in the newer 

 porpiiyries, the dolorites, and the true volcanic formations, which he 

 distinguishes by the term of overlying, unstratified rocks ; and he al- 

 ludes to the assistance which the practical miner would derive from 

 attending to this distinction, and to the principal object of the paper, 

 — the connexion of igneous with metalliferous deposits. 



April 11th. — .\ Letter from George Gordon, Esq., addressed to 

 Roderick Impey Murchison, Esq. P.G.S., noticing the existence of 

 lias on the southern side of the Murray Firth, was first read. 



Mr. Gordon, after referring to the memoir of Professor Sedgwick 

 and Mr. Murchison on the North of Scotland, in which lias is shown 

 to occur on the northern side of the Murray Firth, points out the 

 existence at Linksfield or Cutley-hill near Elgin, of a stratum of clay 

 inclosing thin bands of limestone, and occupying a position analo- 

 gous to that of the lias on the northern side of the Firth. Mr. Gor- 

 don likewise states, that in making the canal to drain Loch Spyine, 

 a bed of clay was penetrated containing numerous specimens of Be- 

 lemnites ; and he conceives that a great part of the bay of Lossie- 

 mouth belongs to that formation. 



A paper was then read " On the strata in the immediate neigh- 

 bourhood of Lisbon and Oporto," by Daniel Sharpe, Esq. F.G.S. & 

 F.L.S. 



Lisbon is shown, by the author of this memoir, to stand upon a 

 range of hills divided by a narrow valley or ravine. The eastern di- 

 vision of the range is stated to be composed of tertiary deposits, and 

 the western of a limestone containing Belemnites, both which are 

 described in the paper. 



The next formation, in a descending order, is a deposit of sand 

 and sandstone, in which no organic remains were noticed. It appears 

 to the north and east of Lisbon, and at Villa Franca, where it under- 

 lies the belemnitic limestone. The celebrated springs of Caldas burst 

 forth in this formation. 



Beneath the sandstone last mentioned, the author observed at 

 Villa Nova da lleinha, to the north of Lisbon, another bed of lime- 

 stone ; but he gives no details respecting its nature. 



The next formation described in the memoir is an extensive deposit 

 of basalt, which is stated to occur in contact both with the tertiary 

 series and the belemnitic limestone, but to have produced no change 

 on these strata at its junction with them. 



The granite of the hill of Cinlra is said to be composed principally 

 of quartz and felspar with a small proportion of mica and hornblende, 

 and to be divided into large blocks by natural lines of cleavage. On 

 the north side of the hill a limestone is stated to rest against the 

 granite, and on the east a dejjosit of shale, and the strata of these 

 formations to be highly inclined, 



2G2 



