183 
TAB. CCXCII. 
SILEX @rotteuns coralliformis. 
Coralliform Quartz. 
Div. 2. Imitative. 
Havine shown some modifications in Limestone and 
Flint separate, it becomes somewhat necessary to show 
them in different substances; and the more so, as they 
have not been noticed by mineralogical writers. Varieties 
of the present sort of specimen have been taken for roots 
of different plants, as Ferns, &c. It is, however, another 
sport of Nature, forming the imitation of one substance 
which is imbedded in another. Thus the Coral is chiefly 
Quartz, and is imbedded in argillaceous Limestone. The 
Quartz in the polished piece is indicated by its taking a 
better polish than the Limestone; for what polishes Quartz 
grinds the Limestone, and will not give it a smooth surface; 
‘and the specimen having been thrown about as a boulder in 
the bed of some river, the Quartz is left beyond the Lime- 
stone, resembling stumps of plants, in many instances not 
much unlike stubble in a lump of earth encompassing the 
roots. I have received pieces from the shore of North Wales. 
This kind nearly resembles M/adrepora musicalis of Lin- 
neus, figured Esper 1. Madrep. tab. 30. 
Tags. CCXCIII is another species, branching like roots 
dividing upwards, as happens in some plants, and the trans- 
verse section would accord with that notion to those not so 
conversant with Corals as with Plants; and in éad. 189 and 
