534 
Proceedings of the Royal Irish Academy. 
to lay it before the Royal Irish Academy, so far as it has yet been pur- 
sued. 
It refers to the occurrence of zinc in magnesian minerals, and in 
rocks containing magnesian compounds. 
1. Chalk. — During an analysis of the white limestone (chalk) of 
the county Tyrone, I chanced to notice the presence of zinc in small 
quantity, although on inspection even with a lens, no trace of any zinc 
mineral could be discovered, and as I could find no analysis of lime- 
stone or other rock in which this metal was given, I thought it worth 
while to notice it at the time.''"-* The first specimen examined was from 
Legmurn, near Stewartstown, county Tyrone. Another was then pro- 
cured from an isolated patch of chalk on the top of Slieve Gallion earn, 
county Derry, about eight miles distant from the first. Zinc was also 
found in this. In both cases it was distinctly reduced by the blow- 
pipe from the powdered rock mixed with carbonate of soda ; but in the 
first specimen its presence was confirmed by a complete wet analysis 
of a large quantity of the chalk — viz., 297*5 grains, the amount being, 
however, too small to estimate. 
2. Basalt. — It then occurred to me to examine the overlying basalt : 
and a specimen N"©. 1, was obtained from a place about 300 yards north- 
east of the chalk quarry in Legmurn. Four or five grains at a time, treated 
with carbonate of soda on charcoal, before Fletcher's hot-blast gas blow- 
pipe, yielded enough of the metal to identify, and the characteristic 
zinc reactions were distinct.f 
I was under the impression at the time that the zinc, possibly oc- 
curring in the chalk as a carbonate, had been brought down from the 
overlying basalt by the infiltration of water; having been originally 
introduced into the latter rock by the same means, alike with the cal- 
careous minerals and zeolites filling up the vesicular cavities in it : but 
this I now believe to have been not altogether the correct solution ; and 
subsequent examination and consideration have led me to what seems 
to be the true clue. 
At the time that the paper containing the account of these analyses 
was read, exception was taken to that part of it which related to the 
existence of zinc in the basalt, on the ground that the metal in ques- 
tion had never been known to occur in rocks of igneous origin ; but as 
I had every reason to believe my analyses were perfectly trustworthy, 
I saw no cause to modify my statement on the objection then put for- 
*ward. Since then, whilst examining — with a dififerent investigation 
in view — a piece of basalt from another locality in the neighbourhood 
of that from whence the first was procured, I succeeded in again find- 
* On the Analysis of White Chalk, &c., with notes on the occurrence of Zinc therein. 
Journal of the Royal Geological Society of Ireland, vol. iii., pt. 3, p. 159. Also Geo- 
logical Magazine, vol. x., No. 10, p. 434. 
f Supra lit. 
