Ch. XXIX.] ISLAND OF MADEIRA. 647 



basalts more or less vesicular, and in some places of trachyte. The 

 lighter tint, c, expresses an accumulation of scoriae, agglomerate, and 

 other materials, such as may have been piled up in the open air, in or 

 around the chief orifices of eruption, and between volcanic cones. This 

 older formation, though represented by an uniform tint, is by no means 

 an amorphous mass, but is separated into innumerable layers which 

 dip towards all points of the compass, so that their mode of arrange- 

 ment could not be expressed in a small diagram. 



The Pico Torres, a, more than 6000 feet high, is one of many 

 central peaks, composed of ejected materials. By the union of the 

 foundations of many similar peaks, ridges or mountain crests are 

 formed, from which the tops of vertical dikes project like turrets above 

 the weathered surface of the softer beds of tuff and scoriae. Hence 

 the broken and picturesque outline, giving a singular and romantic 

 character to the scenery of the highest part of Madeira. North of a 

 is seen Pico Ruivo (c), the most elevated peak in the island, yet ex- 

 ceeding by a few feet only the height of Pico Torres. It is similar in 

 composition, but its uppermost part, 300 feet high, retains a more 

 perfectly conical form, and has a dike of basalt with olivene at its 

 summit, with streams of scoriaceous lava adhering to its steep flanks. 

 There are a great many such peaks east and west of a, which seem to 

 be the ruins of cones of eruption, the materials of some at least having 

 been arranged with a qua-quaversal dip. Among these is Pico 

 Grande, c, fig. 708, now half-buried under more modern lavas which 

 have flowed round it. 



It will be seen that the beds of lava in the central region between 

 e and / (fig. 706, p. 648) are nearly horizontal, or have a dip of no 

 more than from three to five degrees, whereas the angle of slope of 

 the beds between / and h is often seventeen degrees on the southern 

 flank, and usually as much as ten on the northern, or between e and g. 

 The moderate inclination of the lavas between B, A, and R has been 

 caused by the juxtaposition of a multitude of cones which have pre- 

 vented the streams of melted matter from flowing freely from the main 

 axis or lava-shed towards the sea, whether in a north or south direc- 

 tion. The marked prolongation of this gentle slope on both sides of 

 R, and from R to/, may be attributed to the fact that below /there is 

 a very ancient ridge of erupted materials, c, which has formed a bar- 

 rier intercepting the free passage of the central lavas to the sea. Be- 

 tween this secondary buried chain above c or below/ and the higher 

 central chain of scoriae below A, the valley or cavity, d, s, was rilled 

 up with horizontal beds of lava, over which an enormous mass of 

 other sheets of basalt and deposits of tuff, from d to R and from R to 

 / were afterwards accumulated, until at last an aggregate thickness 

 of 3500 feet of stratified materials was formed. Sections of this vast 

 accumulation are exposed to view in nearly vertical precipices in the 

 deep valley called the Curral. But when the lavas had surmounted 

 the ancient ridge below/, and were no more obstructed in their sea- 



