FROM THE KENDAL AND SEDBERGH DISTRICTS. 167 
Layers of calcite, interposed between the cleavage-planes, may also 
be observed, as figured by Prof. Zirkel*. 
Augite.—Associated with the mica, in more or less abundance, is 
a mineral which is herein generally described as augite. In some 
cases it undoubtedly is this mineral, the characteristic section per- 
pendicular to ¢ being very conspicuous ; in others, however, the form 
(at any rate now) is indefinite. The crystal is almost always replaced 
by secondary products. In some (and here we note the external 
form to be, as a rule, better preserved) there is chiefly viridite (a 
feebly doubly-refracting variety, probably delessite or some serpen- 
tinous mineral) ; in other cases calcite or dolomite predominate, with 
some indications of viridite and another secondary mineral (possibly 
also magnesian), which exhibits a rather indistinct microgranular 
structure, and is doubly refracting, showing dull milky-blue tints. A 
somewhat similar result of decomposition in the case of hornblende 
is figured by Prof. Zirkely. 
Calcite is present in many of these rocks, showing the characteristic 
cleavage ; but not seldom associated with it, and sometimes predo- 
minant, is an apparently different mineral, which is more probably 
dolomite. The form of the crystalline grains is more regular, the 
cleavage-planes are less distinctly marked, and the colours more bril- 
liant than is usual in calcite. A study of numerous slides contain- 
ing calcite, and several of dolomitic rocks from various localities, 
among others the Italian Tyrol, seems to prove that dolomite, when 
pure, commonly occurs in rather regular polygonal or rounded 
grains, while in the case of calcite these are irregular. In the 
former the cleavage-planes are less conspicuous than in the latter; 
but the grains, when lying in the right position (with crossed Nicols), 
are beautifully coloured, showing a bright apple-green and its com- 
plementary pink, while the tints of calcite are dull. For these rea- 
sons, which are given at length, as the writer has not seen them 
noted in the ordinary text-books, he considers much of the mineral 
in these mica-traps to be dolomite, to which also we may per- 
haps assign a number of very minute bright-coloured granules which 
are disseminated over the slides. 
Opacite and ferrite are employed in the sense assigned to them by 
Prof. Zirkel+,—the former denoting “ black, entirely opaque, amor- 
phous grains and scales,” which are very frequently metallic oxides, 
especially of iron; the latter ‘“‘ yellowish, reddish, or brownish, 
amorphous, earthy substances, which are not unfrequently pseudo- 
morphous after iron-bearing minerals, probably very often hematite 
or limonite.” We have, however, included in the former term 
grains which are not strictly amorphous, but either rather too 
small or not so placed as to have their form determined with 
accuracy. 
With two exceptions, the mica-traps here described lie in an irre- 
gular band, extending from Windermere to a few miles east of Sed- 
* U.S. Geol. Expl. of Fortieth Parallel, ‘Microscopic Petrography, pl. v. fig. 1. 
+ Loe, cit. pl. iii. figs. 2, 3. 
t Loe, cit. p. 12. 
