Dear Sir,

In the succession of the older formations the species and genera of Trilobites do change, and then they all die out.—¹ To any one who believes that geologists know the dawn of life (i.e. formations contemporaneous with the first appearance of living creatures on the earth) no doubt the sudden appearance of perfect Trilobites and other organisms in the oldest known life-bearing strata would be fatal to evolution. But I for one, and many others, utterly reject any such belief. Already three or four piles of unconformable strata are known beneath the Cambrian; and these are generally in a crystalline condition, and may once have been charged with organic remains.²

With regard to animals and plants, the locomotive spores of some algæ, furnished with cilia, would have been ranked with animals if it had not been known that they developed with algæ.³

Dear Sir | Yours faithfully | Ch: Darwin.

P.S. I am obliged for your very courteous expressions in regard to my work.

W. Horsfall Esq.