MOLLUSKITE. 435 
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, as in the spiral univalve, represented in sec- 
tion, Lign. 139, fig. 3. 
A microscopical examination of the Maidstone molluskite 
detects, with a low power, innumerable portions of the nacre- 
ous laminze of shells, intermingled with the carbonaceous 
matter, many siliceous spicula of Sponges, minute spines 
- of Echinoderms, and fragments of Corals ; these extraneous 
bodies probably became entangled among the floating animal 
matter. A large proportion of the shelly lamine, examined 
with a high power, displays the peculiar structure of the 
Terebratule (see Lign. 126, fig. 2°), of which several species 
are abundant in the Kentish Rag. 
The dark masses and veins so common in the Sussex and 
Purbeck marbles are produced by molluskite. If at the 
period of their envelopment the shells were empty, they 
became filled either with grey marl and limestone, or with 
white calcareous spar ; but if they enclosed the bodies of 
the Mollusks, the soft mass was changed into carbonaceous 
matter ; and in polished sections of the marble, the mollus- 
kite appears either in black or dark brown spots, or fills up 
the cavities of the shells. The dark blotches and veins 
observable in the fine pillars of Purbeck marble in the 
Temple Church, London, are produced by molluskite ; and 
the most beautiful slabs of Sussex marble owe their appear- 
ance to the contrast produced by this black substance in 
contact with white calcareous spar.* , 
Carbon, resulting from animal remains, is of frequent 
occurrence in many strata ; and the fetid emanations from 
* See a “ Memoir on the Carbonized Remains of Mollusca,” by the 
author. Read before the Geological Society of London, February, 
1843; and published in the American Journal of Science, 
