On the '' Porcupine'' -Exiiediiion Madreporaria. 297 



and wandered more than others, and that some have lasted even 

 from the Pateozoic 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 charactei'ized by a number of organisms which 

 are not found in others, and by the gi'ouping of numerous species 

 which are allied to those of preceding and succeeding times, but which 

 are not identical. Certain portions of the world's surface were te- 

 nanted 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 t«rni, 

 the " homotaxis " of certain natural-history provinces during the 

 successive geological ages has been very exact. The species differed ; 

 but there was a philosophy in the consecutive arrangements of high- 

 land and low-laud faunas and floras, and of those of shallow seas, 

 deep seas, oceans, and reef-areas. The oceanic f 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 occur- 

 rence 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 geography of the 

 world which were initiated by the upheaval of the Alps, the Hima- 

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

 still in the Cainozoic or Cretaceous age would hardly be consistent 

 with the necessary terminolog)^ of geological science. 



During the end of the Miocene age and the whole of the Pliocene 

 the Sicilian area was occupied by a deep sea. The distinction be- 

 tween the faunas of those times and the present becomes less, year 

 after year, as science progresses ; and it is evident that a great 

 number of existing species of nearly everj' class flourished before the 

 occurrence of the great changes in physical geology which have be- 

 come the artificial breaks of tertiarj^ geologists. That the Cainozoic 

 deep-sea corals should resemble, and in some instances should be 

 identical in species with, the fonns now inhabiting vast depths, is 

 therefore quite in accordance with the philosophy of modern geologj-. 

 Before the deposition of the Cainozoic strata, and whilst the deep- 

 sea deposits of the Eocene age were collecting in the Franco-British 



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

 t P. M. Duncan, Quart. Journ. Geo'. Soc. No. 101. 

 Ann. & Mag. N. Hist. Ser.4. Vol.y. 20 



