336 
THE GEOLOGIST. 
origin ; that they have not been thoroughly explored ; and also that 
the occurrence of teiTestrial organisms in marine-deposits must be 
the exception, and by no means the rule ; still, it is not easy to 
explain away the facts that nothing analogous to the oceanic mam- 
malia of the existing fauna, or the marine reptiles of the mesozoic 
epoch, occur in these old rocks ; that even fish are not met with 
below the very uppermost beds of the Silurian system; — the "passage- 
beds" between it and the Devonian series — that below the middle 
Silurian rocks are poor in fossils, both specially and individually, in 
proportion as they are ancient ; — fossil-poverty b'l^ing in fact a function 
of antiquity — that the Longmynd rocks, in no respect ill-adapted for 
the preservation of organic remains, have, in all their vast thickness, 
yielded no more than some nine or ten species ; that whilst the 
presence of phosphates may be fairly expected in strata in which 
organisms were once entombed. Professor Daubeny failed to detect 
the presence of any such salts in the Welsh slates ; unless we suppose 
that the most ancient fossiliferous rocks with which we are acquainted 
were coeval in their origin with the earhest introduction of life on 
the globe ; that life was at first, and for a very lengthened period, 
represented in the world by invertebrate animals and comparatively 
humble plants exclusively ; and that there has been, on the whole, a 
progression" from simple to complex forms as we pass from ancient 
towards modern times. 
But even if we provisiorally adopt this doctrine of organic pro- 
gression, it must be with important limitations and qualifications. 
Admitting that the evidence at present before us is to the efiect that 
the invertebrata appeared on the stage of life long before the verte- 
brata ; and that, of the latter fish, were introduced earlier than reptiles, 
which in their turn held sway in the world for a considerable period 
antecedent to the advent of mammals : still the humblest representa- 
tives of each class were not always the first to appear, as, for example, 
in the class Pisces. Amongst the invertebrates, also, the lowly classes 
do not invariably appear earlier, or in greater specific or individual 
development than those of higher rank, as will hereafter be shown. 
It must be remembered also that the argument for progression is 
entirely negative, and would be valueless in the presence of an 
opposing positive fact ; so that, after all, perhaps the only safe 
verdict in the great case of Progression versus Uniformity, is " Non- 
proven." 
Of the classes represented in the Devonian series, Amorphozoa, 
Annelida, CiiTipedia, and Pteropoda, seem to have been specifically 
unimportant, whilst the remainder were comparatively rich in species.* 
Equality in specific wealth in the various classes, however, by no 
means obtains now any more than in the earlier age under con- 
sideration. 
In some cases it appears that classes poor then are still poor, as 
* See Table 2nd column of figures. 
