RIBEIRO COAL OF S. PEDRO DA COVA. 11 



tinuation of the coal-beds in depth, and, therefore, also the geological 

 position which they here appear to possess. 



And, in truth, these coal-beds, so far from belonging to the Lower 

 Silurian formation, as their stratification might appear to prove, and 

 as Daniel Sharpe * has assigned them, are much younger, and must 

 be considered of Devonian or Carboniferous age, as will be shown 

 hereafter. 



The mica-slate and the gneiss composing the first system are well 

 displayed beyond the beds of Oporto and S. Pedro da Cova, without, 

 however, showing a regular connexion or covering a great area. 

 Excepting the Serra da Freita for the mica-slate, and the Valley of 

 Cambra, with the banks of the Caima and the Vouga, for the gneiss, 

 these crystalline rocks everywhere appear more as the results of 

 local metamorphism — produced through the alteration of the clay- 

 slate and talc-slate where those formations were exposed to the in- 

 fluence of the intrusive granite — than as a definite, uniform, meta- 

 morphic formation covering a large superficial area. 



But the azoic talc-slate and clay-slate, besides the extreme uni- 

 formity of connexion and development which they exhibit in the 

 before -mentioned zone, cover large spaces in Portugal, and contri- 

 bute largely to the peculiar features of many districts in that 

 country. We must, therefore, consider that stripe which appears 

 between Oporto and Baltar as isolated, through its being cut off by a 

 mass of granite. This is by no means the case with the fossiliferous 

 beds of the zone in question. Although the fossiliferous beds may be 

 shown to be clearly independent of the azoic group, both in regard to 

 their geographical position as well as their distribution and strati- 

 graphical relations, this cannot yet be done in regard to the relations 

 which the coal-beds show to that fossiliferous group. 



On the contrary, a geographical dependence of the one system upon 

 the other can be recognized, as has been observed in the neighbour- 

 hood of Oporto, Bussaco, and at some places in Beira-Baixa. 



The author then gives some details respecting the lithology, dip, 

 and direction of the foregoing beds of the first and second systems, 

 and of the members of the third system. The latter series he 

 divides into two groups, distinguished by peculiar mineralogical 

 characters and fossil Plants, as well as by the different dips of their 

 individual beds. 



A section from west to east, about the neighbourhood of the 

 Igreja velha de S. Pedro da Cova, through those beds, will show the 

 following series, in ascending order : — 



First group. 



1. Greenish and grey, lustrous slate/dipping from 70° to 80° towards 

 E. 20° N. Upon this slate rest the coal-bearing beds. 



2. Breccia, formed out of the angular fragments of the argillaceous 

 slate which forms the basement-bed of this group (1). 



3. Blackish and very micaceous clay-slate, alternating with thin 

 beds of micaceous sandstone, in which appear also small pieces of 

 felspar. 



* Quart. Journ. Geol. Soc. vol. v. 1849, pp. 146-148. 



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