82 EXCURSIONS IN MADEIRA 



that just described ; then a considerable vertical depth with 

 obhque lines, hke lines of cleavage, on its surface ; where it 

 became harder, covering the chfF with a ragged outhne of large 

 indurated flakes, shooting upwards. I made two sketches, the one 

 when half way down the cliff, the other when on the summit, 

 with my face turned inland, so as to take in the three peaks, 

 Plate 7, A, which are composed of the same tufa, intersected by 

 dikes, which appears between the sandstone and the sea in the 

 other drawing, Plate 7, B'', the sandstone having been deposited 

 on it, only in the lower part of the island, which happens to be the 

 middle. The looser sandstone immediately below the flaky, and 

 which yielded to the fingers, contained, in its upper and outer 

 surface, an ampullina, (or marine ampullaria) a large helix resem- 

 bhng the h. plicata, fig. 17", but differing, from the plate being on 

 the last whorl, which does not advance as far into the mouth ; a 

 still larger, wholly unknown to me, fig. 16, and two others, the 

 one, a helicella of De Ferussac's groupe, marginatte, the other, a 

 helicigona o£ the groupe, vortices'^. I found none of these shells, 

 which were notoriously in a fossil state, deep within the mass, 

 although it does not follow that they are not to be found there ; 

 but some of the upper masses of this loose sandstone on the plain, 

 seemed almost entirely composed, throughout, of a small bulimus, 

 fig. 15, two species of helicella, fig. 13 and 14, each belonging to 

 De Ferussac's groupe, aplostomce, the one perfectly smooth, and the 

 other striated longitudinally. All these shells were quite white. 

 I found no ampullince amongst the shells of the beach, no bulimi 



^ It is of a greenish-grey colour, with orange-red ferruginous spots; it becomes 

 harder upwards, and its specific gravity is 1.95. 



' Since named h. subplicata. Sowerby. — Ed. 



* In examining the beds of sandstone at the northern extremity of the Punta Araya, 

 near Cumana, frequently bathed by the sea, Baron de Humboldt observed univalve 

 shells, resembling the genus helix, mixed with marine bivalves. Voyage, 1. 2, c. 5. 



