326 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [March 22, 



containing corals and sea-shells. These marine strata are elevated at 

 least 1200 feet above the sea. 



A long and complicated series of volcanic eruptions, for the most 

 part subsequent in date to the above, and which took place in the 

 open air, built up the island. They have given rise to a mountain- 

 chain about thirty miles in length, running east and west. This chain 

 in its middle and loftiest portion rises to the height of 5000, and in 

 some peaks to more than 6000 feet. Its composition is displayed in 

 the precipitous sides of valleys more than 3000 feet deep, and is seen 

 to consist entirely of scoriae, lapilli, breccias with angular fragments 

 of volcanic rocks, tuff, scoriaceous lava, and some beds of sohd lava ; 

 the whole being traversed by dikes. None of the fragments of stone 

 in the breccias of the central region have been rounded by water, and 

 no marine remains have been found in them ; hence Sir Charles infers 

 that, had there never been any upheaval, Madeira would have acquired 

 a height of between 4000 and 5000 feet by the simple reiteration of 

 volcanic eruptions above the sea-level, or by the heaping up of ejected 

 materials, which have been fissured, and injected by lava in the form 

 of dikes. Large portions of these mountains, constituting the axis of 

 the island, are amorphous and unstratified ; but a series of basaltic 

 lavas, separated by tufaceous partings (many of which have pro- 

 bably been ancient soils), are seen to dip away in all directions 

 from the central axis, chiefly towards the north and south, where 

 the island is only twelve miles in diameter, but also towards the 

 east and west, where the chain is highest and most dome-shaped. 

 Under a thickness of about 1200 feet of these lavas. Sir Charles 

 Lyell and Mr. Hartung discovered, in the ravine of San Jorge, a 

 leaf-bed, or argillaceous layer full of fossil leaves, both of Ferns and 

 dicotyledonous plants. 



These remains show that the island was clad with a vegetation 

 analogous in many points to that now existing, long before a consider- 

 able part of the volcanic eruptions had occurred ; confirming the 

 opinion derived from the mechanical structure of the rocks, that 

 the eruptions were supra-marine. The plants, according to Mr. Charles 

 J. F. Bunbury, who visited Madeira with Sir C. Lyell, consist of 

 Ferns of the genera Sphenopteris, Adiantum 1, Pecopteris, Wood- 

 wardia, and others, one of them ha\ang the peculiar venation of 

 Woodwardia radicans, a species now common in Madeira. There 

 are also a profusion of dicotyledonous leaves, some apparently of the 

 Myrtle family, the larger proportion of them having their surfaces 

 smooth and unwrmkled, with a somewhat rigid and coriaceous texture, 

 and with undivided or entire margins. " These characters," observes 

 Mr. Bunbury, "belong to the Laurel-type, and indicate a certain 

 analogy between the ancient vegetable remains and the modem 

 forests of Madeira. Li these last. Laurels and other evergreens 

 abound, with glossy coriaceous and entire-edged leaves, while below 

 them there is an undergrowth of Ferns and other plants." 



The lavas and tuffs, which dip away from the central axis, increase 

 in thickness as they recede from it, and become less and less inter- 

 sected by dikes. Near the axis they are usually but slightly inclined. 



