ANKERITE VEINS OF LONDONDERRY—LOUIS. 53 
highly cleavable masses, sometimes white, usually pink or flesh- 
coloured. 
4th.—Calcite—This mineral is found lining fissures in the 
well known form of Dogtooth Spar, and in large, often drusy, 
sealenohedra. It is not, however, a pure Calcite, as is shown by 
the following analyses, the first being that of a specimen of 
Dogtooth Spar, and the second of a large scalenohedron :— 
Tr re, 
InsolublesMatter’ 2iiencc ac os trace. 
CalcieiCarhonatey!s wisis scarce 95.93 90.69 
Ferrous aah eae ney tae ee es 1.45 Bey 
Mancanouse? Fivyyseen-ate 46% 211 1.49 
NEA OMESIG HF Rd i fy+ else cyst eoat os 0.5 4.06 
100.72 99.49 
5th.—Aragonite.—It occurs in acicular crystals, lining fissures 
or cavities in the Ankerite, or implanted upon Barytes or Cal- 
cite. The crystals vary in size from an inch or more in length 
down to microscopic minuteness. Aragonite appears to have 
been one of the last minerals introduced into the vein, as it is 
invariably found investing the others. 
6th.—Iron pyrites occur sparingly in very minute dissemi- 
nated crystals, near the south or hanging wall. 
7th.—Specular ore occurs in thin ie ramifying through the 
Ankerite, and in some places forms a layer about one inch in 
thickness between the Ankerite itself and the hanging wall. 
Veinlets of Specular Ore are also found penetrating into the 
shales on the same side. 
This list comprises all the original mineral constituents, as at 
present known, but in addition to these we have in small quan- 
tities in the upper parts of the veins the decomposition products 
of Ankerite and Sideroplesite, which, from their intimate con- 
nection with the origin of the Londonderry Iron ores, acquire a 
high degree of interest. Whilst all these ores are probably de- 
rived from the decompositions of the Carbonates, the only one 
that shows in its actual structure any proof of such origin is that, 
-known as “ Red ore.” 
