DEPOSITS OF NOETH WALES. 363 



fossils often broken and confusedly huddled together, are the remains 

 of the littoral zone of the same period." 



If we consider how pulpy and gelatinous was the matter of which 

 the creatures were made who swarmed in that early sea, and how 

 light were their horny shells, and contrast these with the density, 

 the compactness, and the high specific gravity of the deposit, 3*25, 

 we shall be able to form some idea as to the length of the period 

 that would be required for the formation of the phosphorite, which 

 in its present greatly compressed state must be many times thinner 

 than the deposit in its original condition. 



Possibly it was in the earlier stages of the process of compression, 

 and when there was but a comparatively light covering of mud 

 above it, that the process of dull crystallization took place, which 

 gathered up the phosphorite into the purer concretionary nodules of 

 the whole deposit. 



If now we were to bend back the edges of the strata at the 

 Berwyn and Cwmgwynen mines, to a horizontal line, and piece 

 them with the middle portion, which has been broken and denuded 

 through the upheaval of the underlying traps and slates — if we 

 further follow the phosphorite bed underground to where it comes 

 up in an altered form on the flanks of Aran Mowddwy, and measure 

 the length of the district described on the map by the breadth 

 thereof, we shall gain some conception of the extent of the shallow 

 sea, with its swarms of life, in which the bed was deposited, covering, 

 as it does, an area of quite 140 square miles. Over this area the 

 depth of the sea must have been nearly uniform, and the same con- 

 ditions of life must have prevailed. Nor do we even now discern its 

 uttermost limits ; for I doubt not, as I have said before, that, in some 

 shape or other, the bed may be found at the same horizon along the 

 entire course of the Bala Limestone. 



It will be observed from the analyses that there is little or no 

 carbonate of lime in the deposit. Yet there are, as we have seen, 

 the remains of shells, whose substance was carbonate of lime, on 

 the uppermost face of the phosphatic limestone which immediately 

 underlies the deposit, showing the existence of these after the 

 phosphatic matter had begun to permeate the limestone in which 

 they are imbedded. Again, we can hardly conceive of a condition of 

 sea-life stretching, as this did, over a large area in which there lived 

 only Mollusks and Crustaceans with horny phosphatic shells and 

 shields. The curious question arises, therefore, What has become of 

 the carbonate of lime of which the shells of their congeners were 

 made ? 



In one of his essays the late Dr. Daubeny tells us that Schmidt 

 found in the inner side of the mouth of Unio and Anodonta no less 

 than 15 per cent, of phosphate of lime, 3 of carbonate of lime, and 

 82 of organic matter, from which the inference was drawn that the 

 phosphate was separated from the blood by this organ for the purpose 

 of cell-formation. The doctor adds, "It seems probable that the 

 carbonate is converted in the animal into phosphate by the phos- 

 phorus it contains." Here, perhaps, we have a clue to the missing 



