436 PROFESSOR HEDDLE ON 
The occurrence of grains of this substance in a metamorphic rock is new, 
frequent as is its occurrence in rocks of an igneous nature ; and the occurrence 
of metallic iron in a rock primarily of a sedimentary nature is difficult to 
explain. Until, however, a laminable, magnetic substance, which precipitates 
a salt of copper, which dissolves in acid without carbonaceous residue, and 
which gives the iron reactions, can be shown to be other than iron, this must 
stand for such. The grains had been protected from atmospheric action by 
a coating of magnetite, a substance lately proposed and patented for this very 
purpose. 
It is perhaps necessary that I should here state that the pounding of this 
chromiferous magnetite under water was executed by the writer himself; and 
that he, upon the observation of the somewhat flattened metallic scales, called 
his assistants to witness the deposition of the copper upon the iron, from an 
acidified cuprous solution. Since the analysis of this Unst specimen, he has 
found metallic iron at a second locality, sheathed also in magnetite. In both 
cases the quantity was so minute as to preclude any examination for nickel ; 
carbon was, however, in both cases absent; and the view entertained by the 
writer is that this is a meteoric dust of iron, which had settled to the bottom 
of the sea, in which its presently containing rock was being sedimented. Such 
a view receives much countenance from the discovery of such metallic dust 
at the bottom of certain oceans explored during the “ Challenger” expedition. 
Lately I have had occasion to examine for His Grace the Duke of Sutherland 
a quartz vein or reef, which occurs at Suisgill. The quartz was seen to con- 
tain ilmenite and magnetite ; but, after crushing, it yielded so considerable a 
quantity of magnetic iron, which rusted with extreme rapidity, precipitated 
copper, and was bruised by a pestle, that I communicated with Messrs. Joun- 
son & Maruey (who had crushed the quartz), as to the possibility of its 
having been abraded from the stamps. The following reply was received :— 
“Tn answer to your letter we beg to state that the sample of mineral sent 
by you was crushed in a cast-iron roller-mill. We do not, however, think that 
any particles of iron became mixed with the ore during the process of crush- 
ing.—Yours, &c., Jounson, Maruey, & Co.” 
I accordingly examined the iron, so far as to quantitatively determine the 
silica and the carbon. Of the first, there was 12°1 per cent. ; of the last, ‘79. 
This being a proportion of carbon very much smaller than any cast-iron con- 
tains, it at least becomes a question if some native iron be not present in the 
rock,—sheathed, like that of Unst, in magnetite. 
