y
needle-like crystals of tremolite, that, from the style of the grouping,
and the contrast existing between the dark green of the enclosed
mineral, and the pale flesh-color of the ground, frequently furnishes
specimens of great beauty. In some pieces the tremolite assumes the
common fan-like form; in some, the crystals, lying at nearly right
angles with each other, present the appearance of ancient characters
inlaid in the rock; in some they resemble the footprints of birds in a
thin layer of snow; and in one curious specimen picked up by Mr.
Swanson, in which a dark linear strip is covered transversely by
crystals that project thickly from both its sides, the appearance
presented is that of a minute stigmaria of the Coal Measures, with the
leaves, still bearing their original green color, bristling thick around
it. Mr. Elder showed me, intercalated among the gneiss strata of a
little ravine in the neighborhood of Isle Ornsay, a thin band of a
bluish-colored indurated clay, scarcely distinguishable, in the hand
specimen, from a weathered clay-stone, but unequivocally a stratum of
the rock. I have found the same stone existing, in a decomposed state,
as a very tenacious clay, among the gneiss strata of the hill of
Cromarty; and oftener than once had I amused myself in fashioning it,
with tolerable success, into such rude pieces of pottery as are
sometimes found in old sepulchral tumuli. Such are a few of the rocks
included in the general gneiss deposit of Sleat. If we are to hold, with
one of the most distinguished of living geologists, that the stratified
primary rocks are aqueous deposits altered by heat, to how various a
chemistry must they not have been subjected in this district! In one
stratum, so softened that all its particles were disengaged to enter
into new combinations, and yet not so softened but that it still
maintained its lines of division from the strata above and below, the
green tremolite was shooting its crystals into the pale homogeneous
mass; while in another stratum the quartz drew its atoms apart in masses
that assumed one especial form, the feldspar drew its atoms apart into
masses that assumed another and different form, and the glittering mica
built up its multitudinous layers between. Here the unctuous chlorite
constructed its soft felt; there the micaceous schist arranged its
undulating layers; yonder the dull clay hardened amid the intense heat,
but, when all else was changing, retained its