yo PROCEBDIJS^GS OF THE GEOLOGICAL SOCIETY. 



accumulated at the present day constitutes the only safe guide to 

 us in interpreting the structures presented by ancient rock-masses. 

 Geologists look forward with much interest to the publication of 

 those volumes of the ^ Challenger ' reports in which Mr. Murray 

 and M. Eenard will deal with these important questions. 



We may especially call attention to two classes of errors which 

 have had much to do with the false conclusions that have been 

 arrived at concerning the conditions under which various deposits 

 have been formed in past geological times. 



In the first place, it has been tacitly assumed that all marine 

 organisms which come from regions bordering the equator must 

 necessarily have lived under tropical conditions. It would be quite 

 as reasonable to treat the mosses and dwarf willows which fringe 

 the eternal snows of Chimboraco and Kilima-iNjaro as tropical 

 plants. Just as mountains rising in Equatorial lands to the limit 

 of perpetual snow exhibit on their slopes every gradation of 

 climate from tropical to frigid, so the depths of ocean, as we now 

 know, exhibit a perfectly similar transition. As we go downwards 

 not only heat, but light also, rapidly diminishes, and many forms 

 which, because they came from Equatorial regions, we have hitherto 

 regarded as tropical, we now know to live in icy-cold water, as 

 well as in almost utter darkness. 



The large size and abundant development of Cephalopods, Crus- 

 taceans, and Eish we now know, from recent deep-sea researches, to be 

 no evidence whatever of the presence either of warmth or of light ; 

 and Sir Joseph Hooker has abundantly shown the fallacy of similar 

 reasoning when applied to plant-life. I feel sure that when the 

 full consequences of these important considerations come to be 

 appreciated, the apparent anomalies of many of the supposed climatal 

 conditions of past geological times will altogether disappear. Eor 

 my own part, I have never felt any difficulty in accepting, as folly 

 equal to the explanation of the facts of the case, the Lyellian doc- 

 trine of chmate being determined by great changes in the relative 

 positions of the land and water of the globe. 



The other cause of misconception with respect to the conditions 

 which must have prevailed during the accumulation of geological 

 deposits consists in the acceptance of an utterly false proposition, 

 which, though seldom formulated, is often tacitly acted upon, namely, 

 " If two organisms exhibit similarity of structure, their environment 

 must have been the same." 



There never has been wanting abundant evidence of the fallacy 



