214 GEOLOGY OF PART OF CUBA. 
to seek which—impelled by a mysterious instinct,—the animal has wandered and toiled 
so far, and has encountered so many perils,—becomes too circumscribed for its accom- 
modation, he is constrained to desert it for some more suitable shell; leaving the discarded 
one, amidst the land shells and the animal exuvie of the caverns, there to form a new 
rock, and a geological puzzle, and to furnish materials for the elaborate speculations of 
some future savan. 
MARINE UNIVALVES SEEN ON LA SILLA. LAND SHELLS OF LA SILLA. 
R. C. Taylor. Examined by Isaac Lea, Esq. 
Trochus Cyclostoma sulcata, . . . . . Lamarek. 
iy Pupa Mumiay o OV retqcor em 
4¥ Caracolla marginata, «» Lams 
Turbo muricatus. Caracolla (2) 
é Flelie microstOma,.: «-a.e° « -«. LOM, 
T Helicogena auricoma. 
Littorina Heélix tusearinimy): =. 0 Ott eee 
Monadonta. Helix-purpurapilae: Sas, 47. a slide: : 
Probably some other species, unobserved. Claueiliaye. 6 et ee go te) 
ADMIXTURE OF FLUVIATILE, MARINE AND LAND SHELLS. 
The shores of the bays of the northern coast of Cuba furnish interesting examples of 
the commingling of shells, the occupants of which had respectively lived under very 
different circumstances. Several streams, for instance, empty into the Bay of Gibara, 
and bring down, during floods, vast numbers of land shells from the high lands. — With 
these are numerous small fresh water univalves, the Neritinia virginea of Lamarck. No 
bivalves were observed in these rivers. Were any geological change to take place, by 
which these accumulated exuvie of the sea, the rivers, and the land, would be consoli- 
dated, as the organic matters are at this moment subjected to in the mountain caves, and 
at some remote period be investigated by a naturalist, he would see here but a repetition 
of the phenomena of supposed estuary deposites, which have more than one parallel in 
remote parts of the globe. 
CORAL ROCKS AND REEFS OF DIFFERENT AGES, 
In the calcareous rocks of Cuba we have seen nothing to countenance an hypothesis of 
a gradual passage, from the submerged reefs of living corals that encircle the island, to 
the older fragmentary coral rock that fringes the coast, at some twenty or thirty feet 
above the sea: and still less to the metamorphic limestone of the interior. We are able, 
in more than one position on the coast, to see, very distinctly, this compact limestone 
dipping below the old coral rock, at an angle of forty-five degrees, northward. Beyond 
the latter extends the reef of living corals; ranging in advance of the coast line, so as to 
leave an intermediate space of shoal water, called the Baao, a quarter of a mile or so in 
breadth, and abounding with fish.* At all times, but particularly when there is a swell 
to windward, the surf breaks with violence upon this reef, so as to be heard many miles 
inland. At low water some of the corals are level with the surface, and others are suffi- 
* Loudon’s Magazine of Natural History, Vol. IX., p. 449. 
