514 FOSSIL PLANTS OF MADEIRA. [Ch. XXIX 



lavas along the great east and west line of volcanic action, that wo 

 find the stony beds in the central region between e and /, fig. 653, 

 nearly horizontal, or having a dip of no more than from 3 to 5 degrees, 

 instead of having a very steep inclination like those in the walls of the 

 Caldera of Palma. 



These level or slightly inclined beds often form platforms, such as that 

 called the Paul de Serra (a, fig. p. 516). But when we recede from the 

 central axis, the lavas acquire an average slope of 10 degrees on the 

 north (as between e and g, fig. 653), and of 15 on the south between 

 / and k. Nearer the sea again, as at i and l, where the most modern 

 lavas occur, the dip diminishes to 5 degrees, and even to 3 J, as at k, near 

 Funchal. In this latter characteristic, however (tie smaller inclination of 

 the lavas near the sea, and their association there with modern cones of 

 eruption, such as m, n, o), there is a strict analogy between Madeira and 

 Palma. Buried cones of eruption also occur at many points, as at p 

 and q, fig. 653, which have been overwhelmed by lavas flowing from the 

 central region. The aggregate thickness of the more solid basalts alter- 

 nating with tuffs rarely exceeds 1500 feet; but below Pico S. Antonio, 

 or r, fig., p. 513, they attain a thickness of 3000 feet, being exposed to 

 view on the sides of a deep valley called the Curral, presently to be 

 mentioned. 



As a general rule, the lavas of Madeira, whether vesicular or compact, 

 do not constitute continuous sheets parallel to each other. When viewed 

 in the sea-cliffs in sections transverse to the direction in which they 

 flowed, they vary greatly in thickness, even if followed for a few hundred 

 feet or yards, and they usually thin out entirely in less than a quarter of 

 a mile. In the ravines which radiate from the centre of the island, 

 the beds are more persistent, but even here they usually are seen 

 to terminate, if followed for a few miles ; their thickness also being 

 very variable, and sometimes increasing suddenly from a few feet to 

 many yards. 



I saw no remains of fossil plants in any of the red partings or laterites 

 above alluded to ; but Mr. Smith, of Jordanhill, was more fortunate in 

 1 840, having met with the carbonized branches and roots of shrubs in 

 some rod clays under basalt near Funchal. Nevertheless, Mr. Hartung 

 and I obtained satisfactory evidence in the northern part of the island, in 

 the ravine of S. Jorge, of the former existence of terrestrial vegetation, 

 and consequently of the subaerial origin of a large portion of the lavas of 

 Madeira. At q in the section (fig. 653) the occurrence of a bed of im- 

 pure lignite, covered by basalt, had long been known. Associated with 

 it, we observed several layers of tuff and clay or hardened mud, in one of 

 which leaves of dicotyledonous plants and of ferns abound. The latter, 

 according to Mr. Charles J. F. Bunbury, are referable to the genera 

 Sphenopteris, Adiantum?, Pecopteris, and Woodwardia, one of them 

 having the peculiar venation of Woodicardia radicans, a species now 

 common in Madeira. Among the dicotyledonous leaves, some are ap- 

 parently of the myrtle family, the larger proportion having their surfaces 



