GEOLOGY OF MADEIRA. 41 



and gray, alternating five or six times, and assuming in its 

 dislocation the form of a how, both the lavas following in a 

 regular bnid the shape of the curve. 



On the left of the stairs by which you are to descend, in- Lava in very 

 numerable small columns of the gray lava project from the ^^^H co- 

 side; they din N. W. and their form in general is quadran- 

 gular; but 1 found severnl of them in prisms of three, five, 

 and six sides. They are remarkably small, and as they lie 

 in this bed, appear almost ail to break off from each other at 

 five or six inches in length, and I never found them exceed 

 this size. They see\T5 to form a dyke that cuts through the 

 horizontal beds of lava. 



At the edge of the descent there is a projection or range Basaltic co- 

 of basaltic columns, rising like a wall, tapering to the top, lu^ns. 

 and separatinsj- into lar<>e quadrangular prisms. We found 

 no black ashes in the valley of the Corral, though toward Volcanic pro- 

 the bottom there are considerable strata of pumice, great ^^^^^- 

 masses of scoria, and cellular lava, and luvain a state of semi- 

 vitrification , the whole presenting evident marks of an erup- 

 tion, 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 toward the sea. Basal- Dip of the 

 tic columns shoot from the side of the ordinary strata, ^^^^^^' 

 which are intersected by various dykes; and one of these in 

 particular swept across both sides of the valley. There are Breccia, 

 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 v/inding staircase, forming the descent 

 into the valley, which was composed of large and small 

 pieces of lav ., some of them of many yards in length and 

 depth, the angles being rounded, and the whole agglutinated 

 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 for ins the base, and these are 

 soft. 



On our road from Funchal to the Corral we saw a stratum Nodules of 



of large nodules or balls of lava, composed of concentric ^^^ l" *^P"' 



... , o . , , . , centric layers, 



layers similar to the coat oi an onion, and lying one above 



another 



