1849.] SHARPE ON THE SECONDARY ROCKS OF PORTUGAL. 137 



form the subject of the following paper : this has been drawn up 

 from my own observations and from a variety of sources mentioned 

 in their places. 



Commencing at the north with the Spanish province of Gallicia, 

 which has been described and roughly mapped by Schulz*, two- 

 thirds of the surface of Gallicia are formed of granite, gneiss, mica- 

 schist, and other crystalline rocks, which cover nearly all the western 

 and middle portions of the province : the eastern side is principally 

 formed of slate, grauwacke, &c., classed by Schulz as Transition 

 Rocks, among which we may expect future observers to find the 

 Silurian and Devonian formations. The strike of the slates varies, 

 but its mean appears to be about N.N.W. There are some small 

 patches of secondary red sandstones and marls scattered over the 

 province, of which the age has not been ascertained ; here and there 

 a small tertiary deposit occurs ; and the bottoms of many of the 

 valleys are filled up with thick deposits of gravel. 



Passing southward into Portugal, we find the same formations 

 continued in nearly the same direction : the greater part of the pro- 

 vince of Minho and the western side of Traz os Montes consist princi- 

 pally of crystalline rocks ; but the rest of Traz os Montes is mostly 

 formed of slates, which are continuous with the same rocks lying on 

 the east of Gallicia. 



With occasional interruptions of slates and other rocks, some of 

 which may perhaps be of more modern date, the crystalline rocks are 

 continued towards the S. or S.S.E., in a band forty or fifty miles 

 wide, through the whole extent of Portugal, from the province of 

 Minho to the banks of the Guadiana, including in their range the 

 great mountainous district of the Serra de Estrella : in this course 

 the granites, &c. gradually slope away from the Atlantic and approach 

 the Spanish frontier, while the slates on their eastern flank slope 

 down into Spain. The wild country occupied by the crystalline 

 rocks oifers few attractions to travellers, and I can meet with no 

 information about it beyond a few notices in the Appendix to Link's 

 Travels f. The highly cultivated district of the Upper Douro, which 

 supplies all the fine port-wines, has been described by Dr. Rebello de 

 Carvalho J ; it is formed of slate-rocks, supposed by that author to 

 belong to the Silurian system, which strike W.N.W. and are nearly 

 surrounded by granitic mountains. 



On the western side of Spanish Estremadura we find the con- 

 tinuation of the crystalline and slaty rocks, which strike about N.W. 

 and are partially concealed by the tertiary deposits of the basin of 

 the Upper Guadiana §. 



The great granitic band above-mentioned is flanked on its western 



* Descripcion Geognostica del Reino de Galicia por Don Guilhermo Schulz. 

 Madrid 1835. 



t Geologische mid mineralogische Bemerkungen auf einer Reise durch das 

 sudwestliclie Europa, besonders Portugal, von F. Link, 1801. 



% Considera9oes Geraes sobre a Constituicao Geologica do Alto Douro, por Joze 

 Pinto Rebello de Carvalho. Porto, 1848. ' 



§ An excellent account and map of this district have been published by Le Play, 

 Annales des Mines, 3rd series, vol. vi. 1834. 



