72 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



siderable depths in icy-cold water ; and, seeing that large marine 

 mammals now live amid snow and ice, I cannot understand why 

 the great marine reptiles may not have done the same. Just as 

 little reason is there for inferring that Sigillarids, Lepidodendrids, 

 and Calamites could only have lived in tropical jungles, as there is 

 for the once popular notion that they flourished in an atmosphere 

 supplied with a very exceptional proportion of carbonic acid ! 



The sooner geologists recognize the fact that all our ideas con- 

 cerning the distribution of the forms of marine life have been com- 

 pletely revolutionized by the discovery that there are cold and dark 

 abysses which are tenanted by numerous organisms having many 

 affinities with those which live in shallow water, — though the 

 latter is warmed by a tropical sun and flooded with light — the 

 more likely will they be to avoid the errors into which we have 

 fallen in the past. Not until the exact distribution of life-forms at 

 difi'erent depths in the ocean has been much more perfectly worked 

 out than it has been at present, will it be safe to reason with any 

 confidence concerning the distribution of extinct types ; and even 

 then we shall ever have to be on our guard against the prevalent 

 fallacy which assumes that analogies in structure are indicative of 

 similarities in the conditions of life. 



And here it may be remarked that the imperfect methods 

 employed on board the ' Challenger ' and most other surveying- 

 ships, leave almost everything yet to be done in the way of deter- 

 mining the limits of depth, temperature, pressure, and other condi- 

 tions under which the different forms of marine life can flourish. 

 It is much to have obtained so great an insight into the characters 

 of some of the creatures inhabiting the deepest parts of the ocean, 

 and of the peculiar conditions which must exist in some of those 

 places where marine life is abundant. But the work which has yet 

 to be done requires the employment of dredges and nets which can 

 be opened when they have reached a certain depth in the ocean, 

 and which can be closed again before being drawn to the surface. 

 Only by the employment of such apparatus can we hope to avoid 

 those sources of error which vitiate all our present generalizations 

 concerning the bathymetrical distribution of the existing forms of 

 marine life. 



When, in addition to these biological studies, we have equally 

 careful determinations of the physical characters of deposits formed 

 at varying depths and distances from the shore, and under diverse 

 influences of tides and currents, we may hope, by combining the 



