128 Mr. D. Sharpe on the Geology of 



outer portions of a soft fine-grained granite with a schistose cleavage. In some 

 places the grain is so fine and the cleavage into rhombs so marked, that the rock 

 might easily be mistaken for sandstone if we were not able to trace the passage into 

 a granite presenting its usual characters. Near Cintra the thickness of this schistose 

 granite is not great, but near the lighthouse it is more considerable, and its pecu- 

 liarity of character more marked. Link*, in describing this neighbourhood, seems 

 in doubt about its nature, and calls it granite passing into sandstone. On the road 

 to the lighthouse are many instances of veins of the hard larger-grained granite in 

 the schistose granite ; but the varieties pass into one another, showing that they 

 were all formed at the same time. 



Toward the western end of the chain, sienitic and porphyritic rocks occur in 

 several places ; and the chapel of the Peninha stands upon the junction of a mass of 

 decomposed felspar-porphyry with the granite. Near Atalaya, I picked up some 

 loose specimens of handsome red porphyry in the bed of a torrent. There is no 

 section of the relative positions of the granite, sienite and porphyry ; but from all 

 I could see, I consider them to have been formed contemporaneously. 



The granite is in several places intersected by veins, particularly near the western 

 end of the chain. Near Atalaya it is traversed by a very thin vein of granite 

 quite distinct from the mass of the rock ; and in a ravine near the same place two 

 veins traverse the granite, one being horizontal, about two feet thick, and of a 

 sienitic character, the other perpendicular and of less importance. Both these 

 veins pass so gradually into the granite, that they must have been formed at the 

 same period with it. Near Cintra I met with a specimen of granite intersected by 

 several veins, some of them not thicker than a sheet of paper ; and they are too 

 thin to have been formed by an injection of granitic matter into a crack. Near the 

 Peninha chapel thin veins of granite traverse the porphyry. 



Faults and Dislocations. 



Near Cintra. (PI. XV. Sect. 1, 2, 4, 5 and 7.) 



Few districts offer such good opportunities of studying the question of elevation 

 as that of Cintra. The granite rises to the height of nearly 2000 feet in one mass 

 of moderate extent and at a great distance from any similar rock, so that the effect 

 which it has produced upon the position of the surrounding strata may be investi- 

 gated as a single problem. 



Sections 1, 2, 4, 5 and 7, show the position of the secondary formations on every side of the Cintra 

 hills ; each of them being drawn in a different direction from the granite as from a centre, so as to show 



* Geol. und Min. Eemerkungen auf einer lleise durch das sudwestliche Europa, p. 59. 



