fiSS Sketci'i of the Geology of Madeira. 



fort of Illhoo it forins with a mass of pumice that is inter- 

 sected with slioht veins of carbonate of lime and zeolite, a 

 rapid angle or curve of declination to the east. To the west- 

 ward of ihe fort, the lava is not found for a little distance, 

 and there is nothing but deep beds of pumice and the ag- 

 glutinated miss above mentioned. These beds of pumice 

 are of various thickness, the deepest appearing to be about 

 four feet, and alternating with that stratum which I have 

 caUcd pepeiirjo. In different cavities of the pumice bed, 

 there are large deposits of black ashes. Tow.irds the ex- 

 tremity of the sinUa the red stone appears on the surface in 

 a more solid state, and lies in prismatic masses, the prisms 

 being small, and not exceeding a few inches in diameter. 

 Their substance is brittle, and crumbles with ease. This 

 stratum of red lava is of a short continuance. Passing a 

 small brook, it dips rapidly to the westward, and in its 

 place the grav lava is found in a confused though some- 

 times prismatic form, and rises liom the beach, while the 

 red lava still runs along the surface to the height of near 

 100 feet, the top being covered with a thick scoria. 



There is also in the vicinity of Fanchal, to the eastward 

 oF the town, a fall of water, which, independent of the ro- 

 mantic beauty of the situation, merits being visited on ac- 

 count of the exposure of the two strata of lava in their re- 

 lative position. The hills are composed wholly of lava, 

 sometimes of a confused, sometimes of a prismatic forma- 

 tion, the red and <rray lavas being visible on both sides of 

 the valley. Near the head of it, a short distance from the 

 cascade, the red stratum is at the bottom, and about 60 feet 

 higher it re-appears, and again, about 200 feet higher, alter- 

 nating with the ^ray lava. The upper red lava dips rapidly 

 to the south, and the strata are disposed in the following 

 wanner: 



Lower Red. 



The rock, down which the cascade falls, is also intersect- 

 ed witli a red stratum of about three feet wide, that traverses 

 it, and dips to the viestward, and is broken off by a broad 



dyke 



