Flora of the SUurian Si/ stem. 123 



shale, and resting on black shale, and (Ji) slates apparently composed 

 of the debris of the chloritic schists on which they rest. The carbo- 

 naceous series is estimated at from 1000 to 1500 feet thick, and is 

 seen on the north bank of the Douro, at Jeremunde, twelve miles 

 from Oporto. North of San Pedro da Cora this series rapidly thins 

 away, and disappears about a mile and a half from that place. 



Having given a detailed account of the rocks referable to the Si- 

 lurian series, noticed by him in Portugal, Mr Sharpe refers to the 

 beds described by Dr Rebello de Carvalha as forming the chain of 

 the Serra de Marao, near Amarante ; those mentioned by M. Schulz 

 on the eastern side of Gallicia, by Link in the province of Tres os 

 Montes, and by Le Play izi Spanish Estremadura, and infers that 

 these also may belong to the Silurian series. 



The lithological characters of the carboniferous deposit of Val- 

 longo, thus plunging beneath beds containing organic remains re- 

 ferred to the date of the Lower Silurian deposits, are important, as 

 shewing the physical conditions under which the accumulations have 

 been effected, and their general agreement with many other deposits, 

 in which sheets of vegetable matter have been so formed, as eventually 

 to have been turned into coal and anthracite, amid mud charged with 

 carbonaceous matter and beds of shingles. Why we should not ex- 

 pect accumulations of the kind at this period, the fitting conditions 

 for the gathering together of plants or their remains, either by growth 

 on the spot or drift from their place of growth, so that they were 

 mixed with little or no common mud or other sedimentary matter, 

 does not appear. We find old mud accumulations, now forming 

 black slates, common enough in some parts of the Silurian series, 

 and there is no want of carbonaceous matter in the black slates of 

 North Wales and Ireland beneath the whole mass of the beds com- 

 monly referred to that series. 



The occurrence of the anthracite beds in the position and under 

 the conditions stated by Mr Sharpe, would be highly interesting in 

 itself, as shewing to what extent clean or nearly clean accunmlations 

 of vegetable matter may have been effected amid deposits in which 

 the carbonaceous, and, we may fairly conclude, vegetable matter was 

 generally more diffused amid mud and gravel ; but the remains of 

 fossil plants detected in connection with this carbonaceous series are 

 still more interesting, always assuming that the sections seen by Mr 

 Sharpe are unequivocal, as his certainly would appear to be, unless 

 we suppose a most enormous reversal of these deposits. 



The remains of the plants found by Mr Sharpo were submitted 

 to the examination of our Foreign Secretary, Mr Bunbury, who, 

 though the specimens of ferns were in bad preservation, considered 

 that one bore a strong resemblance to Pecopteris Cyathea, of the 

 coal-measures ; another reminded him of Pecopteris niuricata, and 

 a third of Neuropteris tenuifoUa. Mr Sharpe calls attention to the 

 evidence, as far as it goes, afforded by these plants, of a vegetation 



