Sketch of the Geology of Madeira. 287 



lliey lie in this bed appear almost all to break oif from each 

 other at five or six inches in length, and 1 never found them 

 exceed this size. They seem to iorm a dyke that cuts 

 through the horizontal beds of lava. 



At the edge of the descent there is a projection or range 

 of basaltic columns, rising like a wall, tapering to the top, 

 and separating into large quadrangular prisms. We found 

 no black ashes in the valley of tlie Corral, though towards 

 the bottom there are considerable strata of pumice, great 

 masses of sconce, and cellular lava, and lava in a state of 

 semi-vitrification; the whole presenting evident marks of 

 an eruption, anterior to that which had formed these various 

 strata of lava, which are visible from the summit of the hill 

 to the bed of the river. 



The dip of the strata is in general towards the sea. Ba- 

 saltic columns shoot from the side of the ordinary strata, 

 which are inlersL-cted by various dykes; and one oFthese in 

 particular swept across both sides of the valley. There are 

 here also rocks of about 100 feet in height, composed of a 

 species of breccia. We examined one near the church, at 

 the extremity of the winding stair-case, forming the descent 

 into the valley, which was composed of large and small 

 pieces of lava, some of them of many yards in lensth and 

 depth, the angles being rounded, and the whole agslutinated 

 together by a hard black earthy substance, that resisted all 

 the force we could use to break off a piece of it. There are 

 other rocks where the red lava forms thy base, and these 

 are soft. 



On our road from Funchal to the Corral wc saw a stra- 

 tum of large nodules or balls of lava, composed of concen- 

 tric layers similar to the coat of an onion, and lying one 

 above another; the stratum exposed was 30 or 4o" feet 

 m depth, and appeared to go down to the bottom of the 

 hill. 



We also examined the coast to the westward of the (own 

 of Funchal. From the beach before the town to Illhoo 

 Castle, and beyond it to the land called the F-'unta da la Cruz, 

 the general character of the coast is as follows: The red 

 stone is the apparent base upon which rests a bed of gray 

 prismatic lava, the stratum being sometimes from 40 to 100 

 leet in depth. At times this gray lava rests upon a deep 

 bed of ashes and pumice, agglutinated together like thepe- 

 perino and puzzvlano in theVicinity of Naples. The scorij^ 

 at the surface is remarkably thick, and all the upper parts 

 of the lava aj^pear to be cellular. Tlic general dip of the 

 lava on the coast iiear Funchal is to the north, but near the 



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