386 HISTORICAL PALEONTOLOGY. 



naked-seeded Flowering plants the Conifers and the Cycads; 

 whilst the higher groups of the Angiospermous Exogens and 

 Monocotyledons characterize the Upper Cretaceous and Ter- 

 tiary rocks. 



Facts of the above nature and they could be greatly multi- 

 plied seem to point clearly to the existence of some law of 

 progression, though we certainly are not yet in a position to 

 formulate this law, or to indicate the precise manner in which 

 it has operated. Two considerations, also, must not be over- 

 looked. In the first place, there are various groups, some of 

 them highly organized, which make their appearance at an ex- 

 tremely ancient date, but which continue throughout geological 

 time almost unchanged, and certainly unprogressive. Many of 

 these " persistent types " are known such as various of the 

 Foraminifera, the Lingulce, the Nautili, &c. ; and they indicate 

 that under given conditions, at present unknown to us, it is 

 possible for a life-form to subsist for an almost indefinite period 

 without any important modification of its structure. In the 

 second place, whilst the facts above mentioned point to some 

 general law of progression of the great zoological groups, it 

 cannot be asserted that the primeval types of any given group 

 are necessarily "lower," zoologically speaking, than their 

 modern representatives. Nor does this seem to be at all 

 necessary for the establishment of the law in question. It 

 cannot be asserted, for example, that the Ganoid and Placoid 

 Fishes of the Upper Silurian are in themselves less highly 

 organized than their existing representatives; nor can it even 

 be asserted that the Ganoid and Placoid orders are low groups 

 of the class Pisces. On the contrary, they are high groups; 

 but then it must be remembered that these are probably not 

 really the first Fishes, and that if we meet with Fishes at some 

 future time in the Lower Silurian or Cambrian, these may 

 easily prove to be representatives of the lower orders of the 

 class. This question cannot be further entered into here, as 

 its discussion could be carried out to an almost unlimited 

 length; but whilst there are facts pointing both ways, it 

 appears that at present we are not justified in asserting that the 

 earlier types of each group so far as these are known to us, 

 or really are without predecessors are necessarily or invariably 

 more "degraded" or "embryonic" in their structure than 

 their more modern representatives. 



It remains to consider very briefly how far Palaeontology 

 supports the doctrine of " Evolution, " as it is called ; and this, 



