16. Trochus, not yet described, but well-known and very common.

17 and 18. Balanus, two species, both common on the coast.

These upraised shells appear to be nearly in the same proportional numbers-
-with the exception of the Crepidulae being more numerous--with those on
the existing beach. The state of preservation of the different species
differed much; but most of them were much corroded, brittle, and bleached:
the upper and lower surfaces of the Concholepas had generally quite scaled
off: some of the Trochi and Fissurellae still partially retain their
colours. It is remarkable that these shells, taken all together, have fully
as ancient an appearance, although the extremely arid climate appears
highly favourable for their preservation, as those from 1,300 feet at
Valparaiso, and certainly a more ancient appearance than those from five to
six hundred feet from Valparaiso and Concepcion; at which places I have
seen grass and other vegetables actually growing out of the shells. Many of
the univalves here at San Lorenzo were filled with, and united together by,
pure salt, probably left by the evaporation of the sea-spray, as the land
slowly emerged. (The underlying sandstone contains true layers of salt; so
that the salt may possibly have come from the beds in the higher parts of
the island; but I think more probably from the sea-spray. It is generally
asserted that rain never falls on the coast of Peru; but this is not quite
accurate; for, on several days, during our visit, the so-called Peruvian
dew fell in sufficient quantity to make the streets muddy, and it would
certainly have washed so deliquescent a substance as salt into the soil. I
state this because M. d'Orbigny, in discussing an analogous subject,
supposes that I had forgotten that it never rains on this whole line of
coast. See Ulloa's "Voyage" volume 2 English Translation page 67 for an
account of the muddy streets of Lima, and on the continuance of the mists