Prof. T. Fuclis on the Deep-sea Fauna. 15 



reef was traversed by cavities, and if we further assume that 

 a Brachiopod fauna of the character of the deep-sea Brachio- 

 poda settled in these cavities, and that finally the cavities 

 were filled up by these shells, together with the washed-in 

 u terra rossa," which, indeed, always occurs upon the free sur- 

 face of coral-reefs, we have exactly those conditions before 

 us which Suss describes in the case of the Dachstein limestone 

 and the Stahremberg beds. 



The interest which the conception of the nature of the deep- 

 sea fauna here advocated possesses for geologists and palaeon- 

 tologists is, however, of a much more general kind. On a 

 previous occasion I have shown that during those epochs 

 through which a warmer climate prevailed at the poles, the 

 temperature-conditions of the sea must have been quite diffe- 

 rent from those of the present day, and that at that time a 

 higher, perhaps even subtropical, temperature must have pre- 

 vailed down to the bottom of the sea. If, then, as was pre- 

 viously supposed, the conditions of temperature had been the 

 governing factor in the bathymetrical distribution of organisms, 

 we could not at once apply the observations which we make 

 at the present day upon the distribution of animals in depth 

 in the sea to previous geological epochs, and in general we 

 should lose all reliable foundation for judging of the faunistic 

 conditions of geological epochs. But the circumstances become 

 quite different when we know that the bathymetrical distri- 

 bution of animals is principally determined not by tempera- 

 ture, but by light, and especially that the distinction which 

 shows itself between littoral and deep-sea faunas has its 

 ground simply in the fact that the former live in the light and 

 the latter in darkness ; for as the behaviour of the sea-water 

 to light has undoubtedly remained essentially the same througli 

 all geological periods, we may also with perfect justice 

 assume that the fundamental features of the bathymetrical 

 distribution of marine organisms have mainly always been the 



same as now. 



As a matter of fact, observation teaches us that the diffe- 

 rence between the littoral and deep-sea faunas which we find 

 in existing seas may be traced back in the same way through 

 all formations ; and, conversely, this fact may also be made 

 use of in its turn as a further proof ol the correctness of the 

 view here advocated. 



