ill. When the great Conglomerate, which is
mainly composed of it here, was in the act of forming, this granite must
have been one of the surface rocks of the locality, and in no respect a
different stone from what it is now. The widely-spread Conglomerate base
of the Old Red Sandstone, which presents, over an area of so many
thousand square miles, such an identity of character, that specimens
taken from the neighborhood of Lerwick, in Shetland, can scarce be
distinguished from specimens detached from the hills which rise over the
great Caledonian Valley, contains in various places, as under the
Northern Sutor, for instance, and along the shores of Navity, fragments
of rock which have not been detected _in situ_ in the districts in which
they occur as agglomerated pebbles. In general, however, we find it
composed of the debris of those very granites and gneisses which, as in
the case of the granitic axis here, were forced through it, and through
the overlying deposits, by deep-seated convulsions, long posterior in
date to its formation. It appears to have been formed in a vast oceanic
basin of primary rock,--a Palaeozoic Hudson's or Baffin's Bay,--partially
surrounded, mayhap, by bare primary continents, swept by numerous
streams, rapid and headlong, and charged with the broken debris of the
inhospitable regions which they drained. The graptolite-bearing
grauwacke of Banffshire seems to have been the only fossiliferous rock
that occurred throughout the extent of this ancient northern basin. The
Conglomerate of Orkney, like that of Moray and Ross, varies from fifty
to a hundred yards in thickness. It is not overlaid in this section by
the thick bed of coarse-grained sandstone, so well-marked a member of
the formation at Cromarty, Nigg, and Gamrie, and along the northern
shores of the Beauly Frith; but at once passes into those gray
bituminous flagstones so immensely developed in Caithness and the
Orkneys. I traced the formation upwards this evening, walking along the
edges of the upheaved strata, from where the Conglomerate leans against
the granite, till where it merges into the gray flagstones, and then
pursued these from older and lower to newer and higher layers, anxious
to ascertain at what distance over the base the more ancient organisms
of the system first appear, and what their character and kind. And
little more than a hundred _yards_ over the granite, and somewhat less
than a hundred _feet_ over the upper stratum