216 



of the surface of the country, since the formation of some of the 

 newest regular strata known in geology. 



March 19th. — Henry Rowland Brandretb, Esq. of the Royal 

 Engineers, Woolwich ; Sir Thomas Phillips, Bart, of Middle Hill, 

 Worcestershire ; and Robert Alfred Cloyne Austen, Esq. of Lin- 

 coln's Inn, — were elected Fellows of this Society. 



Extracts were read from a paper entitled " Reference to a Geo- 

 logical Map and Section of Pembrokeshire, " by Alfred Thomas, 

 Esq., Mineral Surveyor, Haverfordwest. 



The author accompanies the map and section with geological 

 and economical remarks. The map comprehends all that north- 

 ern part of Pembrokeshire not described by Mr. De la Beche, and 

 the section is drawn from St. Gowan's Head on the south to Car- 

 digan on the north. The alternations of the different formations 

 in the county are detailed in a series of descriptive sections : the 

 chief masses are coal measures, including culm and coal grits, 

 mountain limestone, old red sandstone and conglomerate, trans- 

 ition limestone, grauwacke, grauwacke slate. All these, in the cen- 

 tral and southern parts of the county, are traversed by, or alternate 

 with trap rocks which are of various kinds, some being syenitic, 

 others hornblendic and amj'gdaloidal, whilst near Fishguard they 

 are columnar and basaltic. The beds of the stratified deposits are 

 frequently contorted, and their nature altered in contact with the 

 intrusive rocks. The transition limestone contains trilobites. 



The first of two letters addressed to R. I. Murchison, Esq., Sec. 

 G.S. F.R.S. &c " On the Lacustrine Basins of Baza and Alhama in 

 the province of Granada, and similar deposits in other parts of 

 Spain," by Col. Charles Silvertop, F.G.S., was then read. 



The Sierra Nevada, rising to the height of 11,000 and 12,000 feet 

 above the sea, is the culminating point of a number of subordinate 

 mountain groups which form a lofty chain stretching from Anda- 

 lusia on the W.S.W. to Murcia on the E.N.E. and bisecting in its 

 range the kingdom of Granada. 



This chain is composed of a central axis of gneiss and mica schist, 

 with successively overlying zones on each flank of transition and 

 secondary i-ocks, which on the south and along the shores of the 

 Mediterranean are here and there covered with patches of tertiary 

 marine deposits containing Sub-Apennine shells ; whilst on the 

 northern flank of the chain, or towards the interior of Spain, the 

 secondary rocks are succeeded by formations of lacustrine origin, 

 which in the kingdom of Granada occupy two large and separate 

 basins, one near Baza, the other near Alhama. These great and 

 elevated depressions in the secondary rocks, though at little dis- 

 tances from the Mediterranean, are so cut off from that sea by the 

 Sierra Nevada, that their drainage is effected in a north-westerly 

 direction into the Guadalquivir, and thence into the more distant 

 Atlantic. The author describes in detail the basin of Baza, which, 

 traversed by an insignificant stream called the Rio Baza, is sur- 

 rounded upon three of its sides by a secondary nummulite-limestone ; 

 the precise age of which he does not pretend to determine 5 although 



