COAL MEASURES BENEATH ESSEX.
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(far greater in those early stages than anything of which we have
experience), which was brought to bear upon those gradually rising
portions of the crust, which have formed the nuclei of present
continents, before their final emergence above the waters of the
universal ocean. By a series of sketch maps Professor Dana, of
America, attempted years ago to trace the outlines of the growth of
the North American continent from the earliest elevation of the
Archaean region of the Canadian Dominion ; and if we turn our
attention to the European continent, we can trace in a similar way
its gradual growth by deposition of later (stratified) formations
going on pari passu with differential movements of the lithosphere
of this part of the globe, from the earliest elevation of the Archaean
regions of Scandinavia (with Lapland and Finland), continued
through the western flank of the British Isles into Brittany ; while
another region of earliest elevation probably extended through
Auvergne, Central Germany, Bohemia, and Upper Austria. A
portion of the present Spanish Peninsula may perhaps have
formed a third and minor region of elevation.
I have dealt with this matter in papers published back in the
"eighties" in its relation to the distribution of the younger Red
Rocks of Europe (the Permian and the Trias) with the aid of the
writings of some leading Continental geologists, added to my own
observations in Germany and in Britain. We are thus brought to
see that in later Palaeozoic time, that is to say, in the great Carboni-
ferous Period, together with the Post-Carboniferous (the Permian or
Dyas), while the crust of the globe was still thinner than it is now,
the lithosphere must have been in a very unstable condition of
equilibrium, and that, as a rule, those broad belts of its surface,
which formed the margins of the earliest regions of elevation
(being subjected to less hydrostatic pressure than those portions
which served as the beds of the deeper oceanic basins), would furnish
conditions of greatest instability ; that is to say, conditions most
favourable to the relief of the general strain of the lithosphere by up
or down movements. Of such a condition of things we have the
actual record in the general facies of those formations, which consti-
tute the strata of the Carboniferous Period, to the later portion of
which our Coal-measures, as a rule, belong.
The sequence of changes recorded in the rocks of the later
Palaeozoic Period, speaking generally, is as follows (beginning with
the older strata) :