the Neighbourhood of Lisbon. 127 



of the red sandstone and Hippurite limestone, I could not find a single instance of 

 the stratified rocks having been altered by it. The basalt invariably lies imme- 

 diately upon the formation below, without the intervention of any foreign mate- 

 rials ; except in a quarry on the west side of the valley of Alcantara, where a 

 deposit, such as might have been formed by the rolling forward of the mass of 

 basalt, occurs between that rock and the Hippurite limestone. The section is as 

 follows : — 



Hard compact basalt. 



Basaltic clay 10 feet. 



Breccia of ferruginous clay, containing argillaceous pebbles ap- 

 parently calcined 6 — 



Rubble of marl and clay, containing angular fragments of lime- 

 stone and calcined ferruginous pebbles 5 — 



Limestone, quite unaltered. 



The beds of trap interstratified with the slate-clay around Cintra having been 

 described, it is annecessary to recur to them, except to repeat that they are much 

 older than the great mass of Lisbon basalt, and contemporaneous with the forma- 

 tion of shale. 



An eruption of trap-rock at the northern foot of the conical hill on which stands 

 the Moorish castle of Cezimbra, has elevated the Espichel limestone and the red 

 sandstone to a high angle. The rock is an amygdaloid, consisting principally of 

 felspar and green earth. The limestone dips at 70° from the trap on the northern, 

 eastern, and southern sides of the hill, and the red sandstone inclines in the same 

 directions at angles varying from 45° to 60°. (See Sect. 12.) 



The limestone, for the thickness of fifty feet above the trap, is more crystalline 

 than usual. There is nothing to point out the period of the eruption. 



Granitic Rocks. 

 (PL XIV. and PI. XV. Sect. 1, 2, 4, 5 and 7.) 



The range of hills which extends from Cintra to the Atlantic, consists of granitic 

 rocks. Its greatest length from San Pedro to the lighthouse on Cape Rock is 

 about seven, and its extreme width about four miles. The highest points are 

 not 2000 feet above the sea, yet they possess all the picturesque character of alpine 

 scenery. 



The prevailing rock is granite, consisting of nearly equal proportions of quartz 

 and felspar, with a little mica ; but it sometimes contains magnetic iron-ore, disse- 

 minated in small grains. Along the whole chain, the central parts of the hills are 

 formed of a coarse-grained granite, which splits into large irregular blocks; and the 



