BY C. W. DE VIS. 



41 



grouped under at most three or four other specific names. Beyond 

 some surprisingly accurate conjectures of Agassiz respecting the 

 structure, habits, and rank in life of their possessor, no knowledge 

 of their life history was obtained, and it seemed as though nothing 

 further could be known, for as none of the littoral beds subsequent 

 to the deep-sea deposits of chalk yielded a trace of its continuance, 

 the genus was naturally conceived to be extinct. Being extinct it 

 should according to all rule geological never have reappeared, 

 but as if to warn us that a law whose sanction depends on future 

 experience is but a law on sufferance, the fish after a term of 

 oblivion measured by the deposition of the Cretaceous and Ter- 

 tiary beds in all their enormous thickness, variety of conditions, 

 and time consumption, is found lingering in two small rivers at the 

 furthest remove from its original habitats. We are here reminded 

 strongly of a case extremely and very interestingly analogous to 

 that of Ceratodus. In the oolite and chalk rocks everywhere a 

 genus of shells, Trigonia, occurs in specific and individual abun- 

 dance, so much so, indeed, as to give to certain beds a name and 

 character. But beyond the limits of the mesozoic strata Trigonia 

 never appears in the older known parts of the world. It was 

 therefore much to the surprise of geologists that Trigonias were in 

 the course of research found still living in tropical seas, notably 

 in those of Australia. In this case, indeed, the gap has been 

 largely bridged, and the wonder diminished, by subsequent dis- 

 coveries of Trigonias in the Pliocene and Miocene beds of Australia. 

 And so it may happen with Ceratodus, for living in the interval of 

 time it must have been, for living it is now, to declare emphatic- 

 ally the imperfection of the geological record. Living in the 

 interval of space it most probably has been, for it has been 

 discovered in the secondary rocks of Asia as well as Europe. But 

 curiosity is not satisfied with the bare inevitable, or the bare 

 probable, we want to know where and how it has maintained its 

 geological existence ; has it always been the companion of mar- 

 supial life as it was in the beginning, and is now at its end ? 

 Have the marsupial and the fish always lived together in Australia, 

 as would seem to be suggested by the prevalence of oolitic 

 characters in the Australian fauna, or have they perforce, termin- 

 ated on our shores their slow retrocession before the adverse 

 influences which have rendered each step in succession baneful 

 to them ? These are questions for the geologist to answer : the 

 first of them for the Queensland geologist especially. For that 

 answer I fear we must wait till the due distinction is made amongst 

 us between geology and mining survey, and our geological staflf 



