(6

it is known that clouds of dust & sand are raised I think there can be no [illeg] doubt that the dust which falls in the Atlantic does derived come from Africa. How to account for the explain the enigma of the absence of the characteristic African forms & of the presence of two forms from S. America, I will not pretend to conjecture. Finally I may remark, that the circumstance of such quantities of dust being periodically blown during four months, year after year, over so wide immense an area, where the waters of the Atlantic Ocean, in the Atlantic ocean, is interesting, as showing by how apparently inefficient cause, a widely extended deposit may be in process of formation; & this deposit, it appears from the researches of Prof. Ehrenberg, will in chief part consist of fresh-water infusoria Polygastrica & of Phytolitharia.)

List of the species named by Professor Ehrenberg. Those marked with an asterisk, were in the dust collected by myself off St. Jago: those not marked are from the four packet collected by Lieut. James.

Polygastrica Phytolitharia