1865.] Jenkins on Strata identified by Organic Remains. 627 



been contemporaneous with Silurian life in North America, and with 

 a Carboniferous fauna and flora in Africa. Geographical provinces 

 and zones may have been as distinctly marked in the Palaeozoic epoch 

 as at present, and those seemingly sudden appearances of new genera 

 and species, which we ascribe to new creation, may be simple results 

 of migration."* This seems to be pushing the conclusion rather beyond 

 the limits of logical inference, unless geological time is something very 

 different from what the students of Hutton and Lyell have been taught 

 to believe. 



Mr. Seeley, however, with greater enthusiasm and less caution than 

 Professor Huxley, makes the apparently extraordinary statement that 

 " Palaeozoic, Mesozoic, and Tertiary, are convenient fictions.""]" But 

 it is not unlikely that, though he appears to say more, this palaeonto- 

 logist actually means the same as myself, namely, that there is no 

 absolute division all over the globe between rocks of Palaeozoic, Meso- 

 zoic, and Tertiary ages ; for it is conceivable to me that the Maestricht 

 Chalk may have been deposited contemporaneously with apparently 

 Eocene beds in another region, and with apparently Lower Chalk strata 

 in a third. 



The same author begins another memoir J by the, to some, equally 

 startling heresy that " The evidence of a rock's age derived from fossils 

 can never be quite conclusive, and never rank as equal in value with 

 sectional evidence ;" but I imagine that in this instance he must refer 

 to cases where a lithological continuity can be traced, and not to widely 

 separated and totally unconnected sections. It is conceivable that 

 sectional evidence may sometimes be superior to palaeontological ; but 

 I shotdd very much doubt whether it is possible that this should always 

 be the case. I can understand why the presence of certain minerals, 

 which have always before been found to characterize particular deposits, 

 or the existence of certain structural peculiarities, such as have hitherto 

 occurred only in rocks of one period, should determine the age of a 

 stratum at a great distance from its supposed analogues much better 

 than weak or scanty fossil evidence ; but it happens more frequently 

 than otherwise that the palaeontological evidence is very much stronger 

 than either the stratigraphical or petrographical, in regard to the 

 question of correlation with unconnected or distant deposits. 



A fertile source of error in the determination of the synchronism 

 of geological formations lies in the very different depths of the sea- 

 bottoms on which strata of the same period may have been deposited. 

 This refers equally to mineral composition and fossil contents, for 

 while the sediment deposited varies, generally speaking, from the 

 pebbles of the sea-shore, through sand to clay, and thence to the coral- 

 reefs and calcareous deposits of the ocean, so the inhabitants of these 

 different zones exhibit a gradual change, not only in species but also 



* " Address Geol. Soc," 1862, p. 22. 'Quart. Journ. Geol. Soc.,' vol. xxviii. 

 p. xlvi. 



t " On the Significance of the Sequence of Rocks and Fossils." ' Geol. Mag.,' 

 vol. ii. p. 264. 



J " On the Fossils of the Hunstanton Red Rock." ' Annals and Mag. Nat. 

 Hist.,' 3rd ser., vol. xiv., 1864, p. 276. 



