150 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 29, 



period. We have no clear guide to the age of the Sardao red sand- 

 stone ; but from its mineral character and horizontal position, I re- 

 gard it as of secondary origin, and do not connect it with the Silurian 

 formation of Ovar and Estareja. 



I have here described the only beds referable to the Silurian 

 system which fell under my own observation in Portugal ; but rocks 

 resembling in mineral character the clay-slates and sandstones of the 

 Vallongo section have been described by Dr. Rebello de Carvalho as 

 forming the high chain of the Serra de JNIarao near Amarante, and 

 covering the whole of the celebrated wine-district of the Upper Douro, 

 in which all the fine port wines are produced upon the slates ; the 

 line of the granitic boundary being the exact limit to the cultivation 

 of the finer qualities of wine*. 



Similar clay-slates and roofing-slates, accompanied by slaty sand- 

 stones, cover the eastern side of Gallicia according to Schulzf, and 

 are stated by Link to form the greater part of the province of Traz os 

 Montes, both flanks of the great granite chain of the Serra de Es- 

 trella, and a great part of the district enclosed between the Zezere 

 and the frontier of Spain J : and we find similar rocks described in 

 Spanish Estramadura by Le Play§. No one has yet ascertained the 

 exact geological age of these rocks ; but on comparing the descrip- 

 tions given of their position and mineral characters with those of the 

 now-ascertained Silurian formation of Vallongo, it becomes highly 

 probable that future observers will find the Silurian system largely 

 developed throughout these parts of the Peninsula. 



Description of the Organic Remains. 

 IsoTELUs Powisii? (Portlock, Londonderry, &c. pi. 6. fig. 1). 



The specimen consists of the tail and a portion of the last joint of 

 the body, and is not enough to determine the species with certainty. 

 It differs from the specimen figured as Asaphus Powisii in the * Silu- 

 rian System,' pi. 23. fig. 9, but agrees well with Captain Portlock's 

 figure ; if the latter prove a distinct species, the Portuguese trilobite 

 must be classed with it. 



Found in slate at Vallongo near Oporto. 



Ill^nus Lusitanicus, n. s. 



Glabella broad anteriorly and contracted posteriorly ; very convex. 

 Eyes placed nearer the back than the front of the head, about one- 

 third of the length of the head from the back. 



Body of ten rings divided into three nearly equal parts by two deep 

 furrows ; the central portion very convex. 



* Consideragoes geraes sobre a constitui^ao do Alto-Douro. Bv Joze Pinto 

 Rebello de Carvalho. 1848. 



t Descripcion Geognostica del Reino de Galicia por Don G. Schulz. 1835. 



X Geologisclie und Mineralogische Bemerkungen auf einer Reise durch das 

 siidwestliche Europa, besorders Portugal. Von H. F. Link. 1801. 



§ Observations surl'Estraraadure et la Nord del'Andalusie. F. LePlay. Annales 

 des Mines, S-^e s^^je^ vol. vi. p. 297, and pi. 6. 1834. 



