58 EXCURSIONS IN MADEIRA 



decomposition. This conducts us to detached and insulated rocks 

 of columnar basalt, washed on all sides by the sea, and remarkably 

 scoriaceous on the upper part. We then arrive at projecting 

 ridges of basalt, which have preserved the same inchned plane in 

 which they flowed into the sea ; columnar basalt then prevails for 

 some distance at the edge of the sea, and rises to about sixty feet 

 above it. The red tufa afterwards becomes evident, beneath the 

 upper basalt, which is out of the reach of the sea, but columnar ; 

 those are the remains, however, of ridges of the lower, or cellular 

 basalt running out into the sea. These are followed by a fine 

 beach and bay, free from cUffs and elevations, like that in which 

 Funchal is buUt, and owing entirely to no streams of basalt having 

 reached, or flowed towards the sea in that direction. This beach 

 is terminated on the western side by strata of tufa, dipping rapidly 

 to the south ; and between these and the Ribeiro dos Soccurridos, 

 the lower and upper basalt are disclosed with the yellow tufa 

 between them. Before we reach Camera de Lobos, we discover a 

 third alternation of basalt, divided from the second, which we have 

 hitherto called the lower, by a deposit of red tufa. Camera de 

 Lobos lies behind detached rocks and ridges of scoriaceous basalt, 

 and close to it we first remark the basaltic dikes descending 

 through strata of yellow tufa, scoria, and red tufa, all of which are 

 above the basalt. The stupendous chfl" which follows, Plate 4, A. 

 presents a grand slip to the eastward, and the whole depth, a per- 

 pendicular sheet of 1600 feet, is composed of strata of basalt, altei*- 

 nating with red tufa and scoriae, and intersected by numerous 

 basaltic dikes (some of which have been disunited by subsequent 

 shps), running from the top to the bottom. Looking at these 

 frequent alternations, can any one hesitate to give up the hypothe- 

 sis, that the scorice have been produced by a series of volcanic 

 eruptions, which have forced through, covered and scorified the 

 upper surface of the basalt, after the waters had deposited it ? It is 



