Davies — Phosphatic Deposits in Nassau, 265 



matter, several answers have been f^iven. It has been supposed to 

 be derived from immense shoals of fish and other organisms, which 

 crowded the shallows of this limestone sea, and whose remains were 

 deposited in hollows and crevices of the rock. It has also been 

 suggested that the phosphorite owes its origin to the action of car- 

 bonic acid water springs, bringing up phosphoric acid, or phosphate 

 in solution from the older strata below ; and, yet again, that the 

 phosphate was dissolved out of the porphyritic rocks on the surface 

 by the action of carbonic acid water ; and that the absence of fossils 

 from the deposit clearly shows that it is not composed of the 

 remains of organic life deposited upon the sea bed. 



In considering these suggestions it will, I think, be evident that 

 the phosphatic matter was, in either case, derived originally from 

 the older rocks, either by the action of springs from below, or by the 

 decomposition of rocks on the surface ; for we have already seen 

 how full of calcareous matter, in some shape or another, some of 

 those older rocks are, and that they bear traces also of a considerable 

 amount of decomposition. Then the matter might also be derived 

 largely second hand from the remains of former organic life de- 

 posited in the neighbouring subjacent rocks. The question then 

 which remains to be decided is, whether this matter derived from 

 the older rocks in various ways, and held in solution by the water, 

 was deposited pure and simple, or whether it was not taken up first 

 into organic forms, and afterwards deposited as the remains of these 

 upon the ocean floor? No fossils are found in the deposit, but it is 

 possible, it may be even probable, that, if there had been organic 

 life, the structure of its remains would become destroyed by chemi- 

 cal action, just as I have elsewhere shown that the distinctive 

 structure of the organic remains, which so largely compose the bed 

 of phosphate of lime which occurs in the Bala limestone of North 

 Wales, has been almost completely destroyed.^ Indeed, such a sup- 

 position appears to me more reasonable than that of a lifeless sea 

 resting upon a limestone bed. Without saying therefore that all 

 the phosphate of lime derived from the older rocks was absorbed 

 into organic life we may suppose that there was life in the sea of 

 that period, and that, in some measure, these phosphatic deposits are 

 the remains of that life. 



To what geologic period do these deposits belong ? Two answers 

 have been given to this question ; the one refers them to the age of 

 the Lower Devonian beds, and regards them as the remains of 

 Devonian fishes ; and the other assigns to them a Tertiary date. 

 The latter supposition is, I think, the one most in accordance with 

 the general features of the deposit. For, an immense period must 

 have elapsed after the deposition of the limestone to admit of the 

 extensive denudation of the surface, often through unbroken strata, 

 which took place before the phosplioi;ijte began to be deposited ; a 

 period of sufficient length, as it appears to me, to bring the depo- 

 sition down to a much later period than that of the Devonian. 

 And then if we consider the comparative softness of the deposit and 

 I Geological Magazine, 1867. Vol. IV., p. 251. 



VOL. V. — NO. XLVIII. 18 



