300 



On the 6 Porcupine '-Expedition Madreporaria. [Mar. 24, 



periods were perfectly artificial notions — that it did not follow, because 

 one set of deposits was forming in one part of the world, others exactly 

 corresponding to it elsewhere, so far as the organic remains are concerned, 

 were contemporaneous — and that life had progressed on the globe continu- 

 ously and without a break from the dawn of it to the present time. 



The persistence of some species through great vertical ranges of 

 strata, and the relatiou between the world-wide distribution of forms and 

 this persistence were noticed by D'Archiac, De Verneuil, Forbes, and 

 others. The identity of some species in the remote natural-history pro- 

 vinces of the existing state of things was established in spite of the dog- 

 matic opposition of authorities ; and then geologists accepted the theories 

 that there were several natural-history provinces during everv artificial 

 period, that some species lived longer and wandered more thau others, and 

 that some have lasted even from the Palaeozoic age to the present. 



Persistence of type was the title of a lecture delivered by Professor 

 Huxley* many years ago ; and this persistence has been admitted by every 

 palaeontologist who has had the opportunity of examining large series of 

 fossils from every formation from all parts of the world. 



Geological ages are characterized by a number of organisms which are 

 not found in others, and by the grouping of numerous species which are 

 allied to those of preceding and succeeding times, but which are not iden- 

 tical. Certain portions of the world's surface were tenanted by particular 

 groups of forms during every geological age ; and there was a similarity of 

 arrangement in this grouping under the same external physical conditions. 

 To use Huxley's term, the "homotaxis" of certain natural-history pro- 

 vinces during the successive geological ages has been very exact. The 

 species differed ; but there was a philosophy in the consecutive arrange- 

 ments of high-land and low-land faunas and floras, and of those of shallow 

 seas, deep seas, oceans, and reef-areas. The oceanic t conditions, for in- 

 stance, can be traced by organic remains from the Laurentian to the present 

 time, and the deep-sea corals now under consideration are representative of 

 those of older deep seas. 



It is not a matter for surprise, then, that, there being such a thing as 

 persistence of type and of species, some very old forms should have lived 

 on through the ages whilst their surroundings were changed over and over 

 again. But this persistence does not indicate that there have not been 

 sufficient physical and biological changes during its lasting to alter the face 

 of all things enough to give geologists the right of asserting the succession 

 of several periods. The occurrence of early Cainozoic Madreporaria in 

 the deep sea to the north-west of Great Britain only proves that certain 

 forms of life have persisted during the vast changes in the physical geo- 

 graphy of the world which were initiated by the upheaval of the Alps, the 

 Himalayas, and large masses of the Andes. To say that we are therefore 

 * Royal Institution. See also Pres. Address, Geol. Soc, 1870. 

 f P. M. Duncan, Quart. Journ. Geol. Soc. No. 101. 



