The remark of that admirable palaeontologist, Edward Forbes, should never be forgotten, namely, that very many fossil species are known and named from single and often broken specimens, or from a few specimens collected on some one spot.
Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove.
No organism wholly soft can be preserved.
Shells and bones decay and disappear when left on the bottom of the sea, where sediment is not accumulating.