Note 185 — Chapter VIII · GUANO.

With regard to the origin of certain guano deposits, which are of very recent date—e.g., Angamos and Ichaboe—there can be no doubt whatever, because we can witness the process of formation still taking place. It is not so, however, with regard to older deposits, for which some have been inclined to claim mineral origin. The best proof that such deposits owe their origin mainly to bird excrements is the comparatively large quantity of uric acid they contain. On the other hand, the evidence in support of the belief that they are also formed from the remains of the birds themselves and other animals, is to be found in the large proportion of phosphates they contain, and the presence in the deposits of feathers and the fossilised skeletons of the animals above mentioned.