utiful map, I have estimated the areas by cutting out and
weighing the paper, and I find that the metamorphic (excluding the
"semi-metamorphic") and granite rocks exceed, in the proportion of 19 to
12.5, the whole of the newer Palaeozoic formations. In many regions the
metamorphic and granite rocks would be found much more widely extended
than they appear to be, if all the sedimentary beds were removed which
rest unconformably on them, and which could not have formed part of
the original mantle under which they were crystallised. Hence, it is
probable that in some parts of the world whole formations have been
completely denuded, with not a wreck left behind.

One remark is here worth a passing notice. During periods of elevation
the area of the land and of the adjoining shoal parts of the sea will
be increased and new stations will often be formed--all circumstances
favourable, as previously explained, for the formation of new varieties
and species; but during such periods there will generally be a blank
in the geological record. On the other hand, during subsidence, the
inhabited area and number of inhabitants will decrease (excepting on
the shores of a continent when first broken up into an archipelago), and
consequently during subsidence, though there will be much extinction,
few new varieties or species will be formed; and it is during these very
periods of subsidence that the deposits which are richest in fossils
have been accumulated.

ON THE ABSENCE OF NUMEROUS INTERMEDIATE VARIETIES IN ANY SINGLE
FORMATION.

From these several considerations it cannot be doubted that the
geological record, viewed as a whole, is extremely imperfect; but if
we confine our attention to any one formation, it becomes much more
difficult to understand why we do not therein find closely graduated
varieties between the allied species which lived at its commencement and
at its close. Several cases are on record of the same species presenting
varieties in the upper and lower parts of the same formation. Thus
Trautschold gives a number of instances with Ammonites, and Hilgendorf
has described a most curious case of ten graduated forms of Planorbis
multiformis in the successive beds of a fresh-water formation in
Switzerland. Although each formation has indisputably required a vast
number of years for its deposition, several reasons can be given why
each should not commonly include a graduated series of links between the
species which l