fragment is heated in the blowpipe, the black specks are easily fused into
black brilliant beads, which become magnetic,--characters that apply to no
common mineral except hornblende or augite. With the black specks there are
mingled some others of a red colour, which are magnetic before being
heated, and no doubt are oxide of iron. Round two little cavities, in a
specimen of this variety, I found the black specks aggregated into minute
crystals, appearing like those of augite or hornblende, but too dull and
small to be measured by the goniometer; in the specimen, also, I could
distinguish amidst the crystalline feldspar, grains, which had the aspect
of quartz. By trying with a parallel ruler, I found that the thin grey
layers and the black hair-like lines were absolutely straight and parallel
to each other. It is impossible to trace the gradation from the homogeneous
grey rocks to these striped varieties, or indeed the character of the
different layers in the same specimen, without feeling convinced that the
more or less perfect whiteness of the crystalline feldspathic matter
depends on the more or less perfect aggregation of diffused matter, into
the black and red specks of hornblende and oxide of iron.

FIFTHLY.

A compact heavy rock, not laminated, with an irregular, angular, highly
crystalline, fracture; it abounds with distinct crystals of glassy
feldspar, and the crystalline feldspathic base is mottled with a black
mineral, which on the weathered surface is seen to be aggregated into small
crystals, some perfect, but the greater number imperfect. I showed this
specimen to an experienced geologist, and asked him what it was; he
answered, as I think every one else would have done, that it was a
primitive greenstone. The weathered surface, also, of the banded variety in
Figure 4, strikingly resembles a worn fragment of finely laminated gneiss.