336 



THE GEOLOGIST. 



origin ; that they have not been thoroughly explored ; and also that 

 the occurrence of terrestrial 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 being 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 earliest 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 provisionally 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 effect 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, Cirripedia, 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. 



