412 Mr. Greville on the 
appears sometimes like adularia, and confusedly crystallized ; 
often compact, like cipoline or primitive marble; sometimes 
sparry, sometimes granulated, and, on the outside of the vein, 
and near fissures, decomposed, and becoming opaque. In all 
its states, it scratches glass, but not rock crystal, possibly from 
want of adherence of its particles ; and in this it differs from the 
substance of the above lump, which cuts glass and rock crystal 
with great facility. 
This lump, and the matrix of Corundum, appeared to possess 
the same properties as Corundum, when examined by the blow- 
pipe, with the different fluxes. 
The matrix of Corundum having sometimes an appearance 
like adularia and feldspar, I ascertained, by Mr. Hatchett's 
scales, the specific gravity of adularia to be 2,558, and of feld- 
spar 2,555. The Corundum, and the lighter Corundum of the 
lump, cut adularia and feldspar; the latter effervesced, and 
combined with soda, which the former did not. 
It is therefore evident, that the matrix of Corundum, or sub- 
stance of the vein, is a distinct substance from adularia and 
feldspar, and nearly connected with Corundum. 
The matrix or vein contains also a black substance, like 
shorl, which, on closer observation, appears to be hornblende. 
This substance Mr. Garrow had remarked to have the ap- 
pearance of charcoal, and, on that account, he had attributed 
the formation of these strata to the agency of fire. Other gen- 
tlemen, from the appearance of the matrix of Corundum, have 
stated it to be a calcareous vein. 
Mr. Garrow observed, that there ran through the strata in 
which the Corundum was found, veins of a substance like dried 
pitch, apparently on their edge, which separated like a pack of 
