chap, vi.] GEOLOGY. 129 



bouring Isle of Baxio (Porto Santo) leaves no doubt that tbey 

 have belonged to the same period. The latter bed, coming 

 out in the sea board instead of the interior, as at S a .° Vincente, 

 and consequently better situated for access and transport, 

 is alone worked at present, and supplies the lime-kilns of 

 Funchal. Amongst the species of shells observed in it are 

 Cardium, Chama, Conus, Cypraea, Gastrochama, Lithodomus, 

 Pecten, Spondylus, Turritella, Vermetus ; and it contains 

 numerous specimens of very delicately-preserved corals. Be- 

 tween these fossils and the casts of similar fossils from 

 Malta, in the British Museum, there is also an observable 

 correspondence. 



The fossils in both islands are mingled with basaltic pebbles, 

 and in many specimens include them. In my father's collec- 

 tion from the Isle of Baxio is a Spondylus (Gaderopus ?) 

 which carries the marks of its attachment to a basaltic rock. 

 The beds, both in the Isle of Ba\io and at S a .° Vincente are 

 penetrated by basaltic dikes, and are covered by, as well as 

 based upon, basalt, the contact of which has given in many 

 parts to the calcareous matter the crystalline structure of 

 marble. Thus it appears that, after the basaltic rocks had 

 been extensively spread beneath the level of the sea, a period 

 of repose had succeeded, during which, through an area ex- 

 tending from Madeira at least to Porto Santo, a bed of shells 

 and corals had formed upon them, and that this bed was 

 afterwards penetrated and overlaid by an irruption of similar 

 materials, in the course of which it was lifted up at S ao Vin- 

 cente to the height of 1700 feet above the sea level. In the 

 Isle of Baxio, on the western side, the same bed is stated to be 

 not more than 50 feet above the water. A gallery, 6 feet 

 high, has been worked through the islet to the eastward, and 

 there the limestone emerges at an elevation of 400 or 500 feet. 



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