82 DEPOSITS OF PHOSPHATE OF LIME. Tbull. 46. 
Mowddwy. Such large quantities of sulphides and graphite as are 
found in this phosphate bed, according to Davies, seem to show the 
former presence of vegetable life. 
An examination of the analyses given farther on will show that there 
is little or no carbonate of lime in these phosphates. Davies, in speak- 
ing of this fact, says : l 
Schmidt found in the inner side of the mouth of Unio and Anodonta no less than 
15 percent, of phosphate of lime, 3 per cent, of carbonate of lime, and 82 per cent, of 
organic matter, from which the inference was drawn that the phosphate was sepa- 
rated from the blood by th is organ for the purpose of cell formation . 2 The doctor adds : 
"It seems probable that the carbonate is converted, in the animal, into phosphate by 
the phosphorus it contains." Here, perhaps, Ave have a clew to the missing carbonate. 
The great preponderance of phosphatic organisms, with which the period covered by 
the deposit commenced, gradually absorbed and secreted all carbonate of lime, 
whether held in solution in the water or redissolved from the shells of dead mol- 
lusks ; and so, turning it into phosphate, grew and multiplied exceedingly, and be- 
came at last almost sole masters of the position by this appropriation, until the sup- 
ply of carbonate of lime became insufficient for their sustenance, as the mineral con- 
ditions came on under which the overlying shales were deposited. 
It seems possible, however, that the absence of carbonate of lime in 
the Wales phosphate is due to its having been leached out during the 
process of partial metamorphosis to which the bed has been exposed, 
as the effect of metamorphosis is often to segregate from the rock which 
is being acted on the minerals of which it is composed. 
The phosphate bed is often separated into two or three smaller beds 
by thin bands of the underlying limestone. It is always found, how- 
ever, that when the upper one or two beds, as the case may be, run into 
the overlying shale they always run out and the lowest bed is always 
the continuous one. 
The bed immediately underlyin g the phosphate bed is a pure lime- 
stone, often covered on the surface with small brachiopods and other 
fossils. It has an average thickness of 6 inches and contains 15 to 20 
per cent, phosphate of lime. Like the phosphate bed, it is very con- 
tinuous and the two are always found together. It is underlaid by a< 
large series of interstratified shales and more or less fossiliferous lime- 
stones. This formation, known as the Bala limestone, gradually runs 
into the underlying ash beds. 
The phosphate bed is overlaid by a series of fossiliferous shales. 
Those immediately over it have all been phosphatized to a greater or less 
extent, and the more the phosphatization has gone on the more com- 
pletely have all traces of organic life been obliterated. In the overly- 
ing shale at Cwmgwynen, Davies found remains of Echinosplwrites 
balticus, Caryocystites, and other echinoderms, Lingulcv, Modiolw, Theca 
' Quart. Jour. Geol. Soc. London, 1875, vol. 31, pp. 364. 
2 Unio and Anodonta, as well as all other species of the suborder to which they 
belong, are fresh-water forms, while the beds under consideration are certainly of 
marine origin. It is most likely that the phosphate matter came from brachiopods 
and trilobites.— N. S. S. 
(556) 
