peneose.] PHOSPHATES OF NORTH WALES. 81 
pearance. There are numerous remains of animal life in the bod, but 
the whole deposit has been so affected by chemical action that, though 
the traces of organic forms are left, it is often very difficult to distin- 
guish them. Still Davies 1 has recognized the remains of Modiola, 
Avicalopecten, Orthoceras, Orthis, Lingula, and trilobites, besides traces 
of many other species. 
Fig. 33. Section of strata at Berwyn phosphorite mine, west of Llangynog, North "Wales; after 
D C. Davies, Geological Magazine, London, 1875. Scale: 1 inch = 32 feet. 
M. H. Johnson, 2 who has made numerous sections of the Korth Wales 
nodules, has found that many of them contain a species of sponge. He 
has also found in the nodules fragments of mollusk and crustacean 
shells, with bodies looking like Coscinopora. From these observations 
he concludes that the nodules are of organic structure. It seems more 
likely, however, that the nodules resulted from the phosphatization of 
a calcareous bed, which may have contained the organic remains dis- 
covered by Mr. Johnson in the nodules. Davies thinks the bed repre- 
sents the remains of an old Laminarian zone and that it originated by 
the phosphatization of calcareous matter by the phosphates from animal 
matter and seaweed. 
The nodules have been so affected by heat and chemical action that 
they often are found blending and running into each other. They some- 
times blend gradually with the matrix, the whole bed assuming a shaly 
structure, so that it is often impossible to draw a distinct line of divis- 
ion. The mass of the stratum is sometimes found to have a very sim- 
ilar composition over large areas ; but where the underlying bed be- 
comes more arenaceous the nodules become much poorer in phosphate 
and richer in siliceous matter. 3 Thus, at Green Park, the bed averages 
only 20 per cent, phosphate of lime. The phosphate stratum, in some 
places, contains numerous concretions and crystals of sulphide of iron, 
which rust on exposure to the atmosphere, thus changing the color of 
the bed from black to brown. The phosphate of lime is itself often 
replaced by these sulphides. Such is the case in many parts of the 
western outcrop of the bed, especially on the flanks of Mount Aran 
l Geol. Mag., vol. 4, London, 1^67, pp. 251-253. 
2 Ibid., vol. 2, d. s., 1875, p. 238. 
3 This is a strong argument for the theory of the formation of the nodules by tho 
phosphatization of the underlying bed. 
Bull. 46 6 (555) 
