CHALK MARL. 157 
various modifications of siilpliuret of iron, and crys- 
tallized carbonate of lime. 
1. Crystallized carbonate of lime. 
This mineral is frequently semi-diaphanous, vary- 
ing in colour from a lightish grey to a gall-stone 
yellow. It occurs in inconsiderable veins, and occa- 
sionally in groups of crystals, lining the cavities of 
the marl : the usual form of the crystal is that of 
an acute rhomboid ; of this kind some interesting 
specimens have lately been discovered at Hamsey. 
2. Sulphuret of iron, or iron pyrites. 
This substance, from the deconq)osition of its 
surface, is generally of a yellowish rusty brown 
colour externally. It occurs in a variety of irregu- 
lar fantiistic shapes, and oftentimes bears the im- 
pression of organic bodies, forming casts of terehra- 
tulcBy pectenites^ madveporites^ and the inner volu- 
tions of scaphites. Small spherical masses with an 
elongated stem, their surface beset with obscure 
pyramidal crystals, and exposing a brilliant radiated 
structure internally, are not uncommon. One spe- 
cimen in my possession contains, within a cavity, 
small crystals of sulphate of lime. 
Crystals of pyrites terminating in the quadrangu- 
lar pyramid of an octohedron, and disposed in irre- 
gular groups, are often imbedded in the casts of 
ammonites and other fossil remains ; and the marl 
pits at Hamsey contain masses of this mineral, 
bearing the form of a species of EscharOy somewhat 
resembling E. foUacea. 
3. Oxide of iron, in the state of a reddish brown 
powder, is frequent in cavities of the marl, and has 
])robably been produced by the decomposition of 
