Sir

I have been very much pleased to hear through D^r. Dieffenbach that you have found some of D^r. Hooker’s & my specimens of service to you. D^r D. tells me that the dust off the N.W. coast of Africa consists of Infusoria: I am truly astonished at this, & I write now to inform you that I have specimens from several other stations in the same sea-region. There can, I think, be no doubt, that it is the finer matter blown from the dry country along that coast. From fusing under the blowpipe easily into a slag, it has generally been thought: to be fine [illeg] ashes from some active volcano. The dust falls during a great part, or all the year over very many hundreds of square miles of sea, & as no great rivers debouch on this coast, there must be a considerable deposit in progress of formation, which, it now seems, will consist of Infusoria. I have always intended drawing up a brief account of the area, over which, this dust falls. Should you like to have this little notice to communicate together with your account of the Infusoria contained in the dust, I shall be very proud to send it, with other specimens, if you choose, of the dust. If you sh^d not care to have my notice, perhaps you would kindly take the trouble to let me know the names of the Infusoria, which you have found in the dust in order that I may refer to them, in the notice, which I will publish in some English Journal.¹

Should you wish for any more specimens or substances in which to look for Infusoria, it will give me great & undivided pleasure to search my collection, although this will take me some time.— It is, however, probable that you are already overwhelmed with specimens from all quarters of the world. D^r. Hooker will be happy to send you any more antarctic specimens, which you would specify.— If you wish for any more specimens, perhaps you will be so good, as to direct me to what countries are most interesting to you, & what sort of substances will be most favourable— Would lignite or imperfect coal; or lumps of old coral from sea-beaches; or corallines & seaweeds from T. del Fuego, be likely.

In case you sh^d wish for any more specimens, could you direct me any cheap way to send them, as I found the carriage of the last Box expensive.—

Believe me Sir | With the highest respect | Your obliged & faithful sevt. | C. Darwin

P.S. | I believe there are many soundings (i.e. the mud & sand brought up on the lead) from great depths in the Antarctic & other seas, at the Admiralty: would portions of these be of service to you, for I daresay they could be obtained?