80 
DEPOSITS OF PHOSPHATE OF LIME. 
[BULL. 46. 
AMORPHOUS NODULAR PHOSPHATE DEPOSITS OF NORTH WALES. 
The rock phosphate deposits of North Wales belong to the Caradoc 
and Bala group of the Cambro Silurian or Lower Silurian formation. 
They immediately overlie the Bala limestone beds and are overlaid by 
fossiliferous shales, sometimes more or less calcareous. They belong 
to the class of rock phosphates, or phosphates having no definite chem- 
ical composition, and are remarkable as being, geologically, the oldest 
of the commercially important phosphate beds which still preserve the 
remains of organic life. 
The phosphate bed has been traced by Mr. D. 0. Davies from the 
town of Llanfyllin to the hills north and west of Dinas Mowddwy. 1 Mr. 
Davies has calculated that the area already known to contain this bed 
amounts to almost 140 square miles, and he thinks it will probably be 
found wherever the Bala limestone occurs. 
t,t'U<i<ltitt(('<ti'{t't<<'i(il/littttfltttuMnt<lit/t'(i(«tttn«<i<<;f<« 
Fig. 32 
after 
Section of strata at Cwmgwynen phosphate mine, southwest of Llangynog, North Wales; 
D. C. Davies, Quarterly Journal Geological Society of London, 1875. Scale: 1 inch = 80 feet. 
As will be seen from the sections (Figs. 32 and 33), the formation in 
which the phosphate bed occurs has been much twisted and contorted. 
In fact, the phosphate bed, wherever found, is in an almost vertical po- 
sition. It varies from ten to fifteen inches in thickness and consists of ai 
mass of black nodules, varying from the size of an egg to that of a co- 
coanut, " closely packed together and even running into each otherJfl 
The nodules are cemented into a solid mass by a black matrix, and the 
whole mass gives an average of 46 per cent, phosphate of lime, while' 
the separate nodules sometimes contain 64 per cent. The bed contains- 
considerable graphite, which gives the black color to both the nodules- 
and the matrix and often gives the former a polished and glossy ap 
'Geol. Mag., vol. 2, London, 1875, p. 183. 
(554) 
