88 DEPOSITS OF PHOSPHATE OF LIME. [BULL.4d. 
scopic smallness to masses weighing four pounds. It occurs adhering 
to the surfaces of Syphonce, corals, and shells, and appears to have once 
been in a plastic state. This substance has been called by Dr. G. A. 
Mantell x " molluskite," and he considers it the remains of the soft parts 
of mollusks. In describing it he says : 
This substance is of a dark-brown or black color, and occurs either in shapeless 
masses, which are irregularly distributed among the shells and other organic remains, 
in sandstone, limestone, etc., or as casts of shells, or occupying their cavities. * * * 
Upon analysis this substance is found to contain a large x>roportion of animal carbon. 
The rocks of firestone at Southbourne, on the Sussex coast, are mottled with brown 
molluskite aud hard amorphous concretions, consisting of carbon and phosphate of 
lime, mixed with sand and other extraneous matter. Casts of shells of the genera 
Venus and Area, etc., entirely composed of the same kind of materials, are also 
abundant in those rocks. * * * The gelatinous bodies of the Trigoniw, Ostrece, 
Ilostellarice, Terebratulce, etc., detached from. their shells, may have been intermingled 
with the drifted wood in a sand-bank; while in some instances the animal matter 
would remain in the shells, be converted into molluskite, and retain the form of the 
original. 
Both Mr. Fisher 2 and Mr. Sollas. 2 who have spent considerable time 
in studying the nodule bed of the Upper Greensand, concur in the 
belief that the nodules are not of either concretionary or coprolitic ori- 
gin, but are composed of phosphatized animal matter. In this belief 
they agree with the theory of Dr. Mantell in its most important poiut. 
Many of the nodules are traversed by shrinkage cracks and wrinkles 
and have a peculiar granulated surface like that of leather. Mr. O. 
Fisher says : 
On the whole a microscopical examination of these bodies rather recalls me, so far, 
to my original opinion that they were sponges, while at the same time it must be 
admitted that in their external appearance they much resemble Alcyoiiaria. 
It is often found that the nodules are richer in their exterior part than 
in the interior. Thus Professor Way found the following results in an- 
alyzing different parts of a spongoid body : 3 
Exterior J 32.27 per cent, phosphate of lime. 
( 61.71 per cent, carbonate of lime. 
Intermediate... J 13.87. per cent, phosphate of lime. 
( 67. 14 per cent, carbonate of lime 
Interior J 10.26 per cent, phosphate of lime. 
c 67.17 per cent, carbonate of lime. 
Such results have been found to hold true with many other phosphates 
and show, beyond a doubt, that the phosphatization went on from the 
outside towards the interior. As regards the internal structure of 
some of these nodules, Mr. Sollas says: 4 
Thin sections examined under the microscope vary from colorless to yellowish 
brown when transparent, but sometimes they are almost opaque from included earthy 
1 Medals of Creation, vol. 1, p. 432, 
3 Quart. Jour. Geol. Soc, vol. 29, London, 1873. 
3 Jour. Roy. Agric. Soc, 1848. 
4 Quart. Jour. Geol. Soc, vol.29, London, 1873. 
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