184 
SUSSEX MARBLE. 
of the Weald clay in England, occurs in layers that 
vary from a few inches to a foot or more in thick- 
ness, and are separated from each other by seams 
of clay, or of coarse friable limestone. 
POLISHED SLAB OF SUSSEX MARBLE. 
This limestone is of various shades of bluish 
grey, mottled witli green, and ochraceous yellow, 
and is composed of the remains of freshwater uni- 
valves, formed by a calcareous cement into a beau- 
tiful compact marble. It bears a high polish, and 
is elegantly marked by the sections of the shells 
which it contains ; their constituent substance is a 
white crystallized carbonate of lime, and their 
cavities are commonly filled with the same sub- 
stance, presenting a striking contrast to the dark 
ground of the marble. In other varieties the sub- 
stance of the shells is black, and their sections 
appear on the surface in the form of numerous lines 
and spiral figures. Occasionally a few bivalves 
( Ci/clas') occur, and the remains of the minute 
crustaceous coverings of the Cj/pri.s faba very con- 
stantly. 
