PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 37 
altogether inverted, being in the Scottish lepidomelane as 1 to 5, and in the 
Irish as 1 to 9. 
A consideration of the foregoing tabulation also makes manifest the follow- 
ing additional chemical distinctions between these minerals. 
Biotite differs from Haughtonite in containing an amount of magnesia which 
is twice as great as that of the protoxide of iron ; the iron also is in Biotite 
present almost solely in the ferrous state; while in Haughtonite the relative 
proportions of the above protoxides are fully more than inverted, there being 
also a considerable quantity of iron in the ferric state. 
In all, the alkalies and water are present in about the same amount ; nor do 
the proportions of the silica and alumina differ largely. 
Altogether, there can be no question that the substance standing in an 
intermediate position in the table is distinct; and I conceive that it is most 
fitting that it should be named after the gentleman who first analysed the black 
micas of Ireland, and so established the specific individuality of the mineral 
which stands next to this in the system,—happily fitting also, seeing that it 
exists as the distinctive mineral of one of the varieties of granite, a rock in 
the study of which Dr Havcurton has for long been closely engaged. 
The geognostic position of these minerals is for the most part well marked. 
As the plates or crystals in which they are found are usually of extreme 
tenuity, it is not easy to obtain, under the ordinary circumstances of local 
collecting, a sufficiency for analysis, and hence the unimpeachable evidence 
afforded thereby is not great in amount; nor is it, in the absence of charac- 
teristic specimens, easy to distinguish between the three species. The instances, 
however, that I shall adduce in addition to those analysed, have, for the most 
part, been established by partial examination or fairly satisfactory proof. 
Every case in which there is doubt will be notified. 
The four first analyses show Biotite to occur in association with granular 
limestone. In Glen Urquhart, in a most peculiar granitiform belt in the centre 
of the lime ; * also, near Milltown, in a singular rock, in association with edenite 
and Wollastonite ; at Loch Laggan, imbedded in chlorite, in the lime; at Shin- 
ness, immediately in contact with sahlite, &c., at the junction of the lime with the 
inclosing rock; at Glen Beg, in contact with two known and a new felspar ;— 
these may together have formed a belt similar to that at Urquhart. Additional 
limestone localities are the following :—In the most westerly of the two great 
beds which traverse the North of Scotland, I only know of it at Redhythe, 
where it is associated in the limestone itself with talc, pyrrhotite, and rutile. 
In the most easterly it occurs at Glen Gairn, with prehnite and coccolite, at 
* This peculiar granitiform belt I have seen cutting limestone strata elsewhere in Scotland,—as at 
Laggan near Dulnan Bridge, Inverness-shire ; and Boultshoch, in Aberdeenshire. This belt always 
carries Biotite, and the felspar in two of these cases has upon analysis proved to be Andesine. 
VOL. XXIX, PART I. K 
