AND PORTO SANTO. 83 



any where, and the existing helices (thickly strewed over the soil 

 formed by the calcareous tufa, and found very sparingly on the fig- 

 trees in the sandy plain), were specifically chstinct from the con- 

 siderably smaller ones, forming entire masses of the loose sand- 

 stone ; and generically distinct from the enormous species imbedded 

 in its surface ^ 



The flaky sandstone frequently formed isolated ledges, or 

 hillocks, of a most picturesque appearance, on the southern part 

 of the plain, numerous flakes being regularly piled on each other, 

 shooting upwards from the soil in angles of 45°, and seeming 

 to emulate the lofty peaks of tufa behind them, Plate 7, A'. 

 Imbedded in these hillocks are numerous, close-grained, indurated, 

 cornuform, hollow masses, with smaller lateral branches, which 

 I conceive to have been formed by the sand having enveloped 

 plants or fragments of wood, subsequently and entirely decom- 

 posed. These sands have evidently been thrown up by the sea, 

 on the low southern coast of the island (almost on a level with it), 

 and have been gradually advanced, and propelled inland, and 

 afterwards more or less agglutinated, until they have reached the 

 northern side, enveloping the vegetation, and entombing the 



" The recent shells which I found on the beach of Porto Santo, were a cyprcBa, a 

 cassidaria, of an orange-colour ; three species of colombella, a trochus of a dusky 

 ground, and spotted with a dull red ; three pecHnes, one spotted with red, another 

 brown, streaked with white and rose-colour, and the shell remarkably thick in 

 texture, (probably a variety of the p. Jlexuosus) and fig. 20, of a pale colour, mam- 

 millated and shaded with light green j four species of venus, one white with brown 

 streaks, and a rose-coloured apex, fig. 19, a second of a pale flesh-colour, and another 

 of the same colour, but nearly transparent, also one of a flesh-colour with rich brown 

 streaks; fig. 18, the cardium edide, a small halyotis, of a deep red, with green and 

 orange streaks ; perhaps a variety of h. tuberculosa, and a rose-coloured echinus, 

 streaked with purple, and with a brown spot at the insertion of each spine. 



'' According to M. Beudant, the basaltic tufas of Tihany are covered by a sandstone 

 resembling the silex molaire of the Environs of Paris. 



M 2 



