TOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 36 1 



Other gentlemen, 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 cards. It is a brown micaceous substance, which in drying 

 foliates, and shows a certain degree of regular arrangement of the component parts ; 

 in this case, the fragments of the folia subdivide, with some degree of regularity* 

 into rhombs, whose angles are 6o° and 120° : it is more smooth, and less flexible, 

 than pure mica. These are all the sorts of corundum which I procured from India. 

 I now proceed to the result of my inquiries in China. 



I requested Capt. Cumming, in 1786, at that time commanding the Company's 

 ship Britannia, to take a specimen of corundum to China, to ascertain its nature, 

 and to obtain specimens, if possible, adhering to their matrix, and regularly 

 crystallized. On his arrival at Canton, he collected the information I wished, with 

 the good sense and zealous desire which he always exerts for his friends. He ascer- 

 tained that the stone I inquired for, was in common use with the stone-cutters ; and 

 he brought me the stone, in its rude and in its pounded state, taking care to select 

 the most regularly crystallized pieces, and others adhering to the rock. A stone- 

 cutter was sawing rock crystal with a hand-saw, which he also brought to me ; it is 

 a piece of bamboo, slit, about 3 feet long, and 1-J inch broad, thickened at the 

 handle by a piece of wood, rivetted with 2 iron pins ; having a lump of lead tied 

 with a thong of split rattan, steadying an iron pin, on which the ends of a twisted 

 iron wire is fastened, which, being 6tretched to the handle, is passed through a 

 hole in the bamboo, with the superabundant wire ; a wooden peg, being pressed 

 into the hole, keeps the bow bent, and the wire stretched, and serves to coil the 

 superfluous wire, till, by sawing the crystal, the stretched wire is worn, and re- 

 quires to be renewed from the coil. The twisted wire answers the purpose of 

 a saw, and retains the powder of corundum and water, which are used in this 

 operation. Dr. Lind had before brought specimens similar to the above, from 

 China. 



From Sir Jos. Banks I obtained Dr. Lind's specimens, and some in powder, 

 which Mr. Duncan, supercargo in China, had sent him, with the Chinese name, 

 pou-sa. The matrix, being mixed with a red and white sparry substance and mica, 

 is generally called red granite : but it appears to me of the same nature as the 

 matrix of corundum from India. The white is more fibrous, and like cyanite ; the 

 red part of it is compact and opaque ; other parts appear to foliate, and pure mica 

 is in considerable patches, and generally adheres to the crystals. This corundum is 

 of a darker brown, and is more irregular on the surface than the corundum of the 

 coast, and is often mixed with black iron ore,* attractable by the magnet. It is 



* A small group, consisting of 3 or 4 octoedral crystals, presents the least common variety of this kind 

 of iron ore : the edges of the octoedra being replaced by planes which almost cover the triangular planes. 

 Rome de l'lsle. Cristallog. vol. 4, pi. 4, fig. 6*9. — Orig. 



VOL. XVIII. 3 A 



