U2 EXCURSIONS IN MADEIRA 



level which the oysters, and marine shells, found 300 miles inland 

 in the blue mountains of America, would seem to indicate ; for the 

 deposit (extending about three-quarters of a mile in each direc- 

 tion) is bounded by hills and small peaks, rising several hundred 

 feet above it, composed of the same tufa on which the sand and 

 shells are deposited, and in the soil of which this small forest must 

 have been growing, thus ; which peaks and elevations present 



no traces of sand on their surface, or elsewhere, above the highest 

 level of that in the flat, i. e., above 250 feet or thereabouts. Seek- 

 ing for that explanation which rests on the fewest and the 

 simplest causes, it occurred to me, when I first reached this bed of 

 sand, (which was on the southern side, where it is level with the 

 water's edge) that there might have been no irruption or elevation 

 of the level of the sea, but a subsidence of the tufa strata (like 

 that of the shores of Alexandria, which, according to Dolomieu are 

 a foot lower than they were in the time of the Ptolemies), the 

 natural consequence of gravity, or one of those slips so frequently 

 evident along the coast, which led to a deposit of calcareous sand 

 on the border of the sea, — which sand, from its extremely fine 

 o-rain, was readily dispersed by the winds, until it reached the 

 north side of the island (for it is barely three-quarters of a mile 

 broad on this part), where the drift line of the sand, with the tufli 

 on which it rests, is about fifty feet above the sea. But then, 

 should we find the marine shells in such heaps at the height of 

 250 feet ? — would the sand have been so firmly agglutinated, as it 

 is in the indurated sheaths which envelope the trunks and bran- 

 ches of the trees?— and could there be a regular, or dip line 



