Professor J. E. Marr— Address. 475 



this hypothesis, the objection raised by Messrs. Gray and Kendall, 1 that in 

 the case of the Pleistocene Ice Age " the cold conditions came on with 

 extreme slowness, the refrigerations being progressive from the Eocene 

 period to the climax," seems to me to be a fatal one. At the same time, 

 rather than asking with the above writers "the aid of astronomers and 

 physicists in the solution of this problem," I would direct the attention of 

 stratigraphical geologists to it, believing that, by steady accumulation 

 of facts, they are more likely than anyone else to furnish the true clue to 

 the solution of the glacial problem. 



I have elsewhere called attention to marked changes in the faunas of the 

 sedimentary rocks when passing from lower to higher levels, without the 

 evidence of any apparent physical break, or any apparent change in the 

 physical conditions, so far as can be judged from the lithological characters 

 of the strata, and have suggested that such sudden faunistic variations 

 may be due to climate. 1 refer to the matter as one which may well 

 occupy the attention of local observers. 



One of the most interesting points connected with climatic conditions is 

 that of the former general lateral distribution of organisms, and its 

 dependence upon the distribution of climatic zones. The well-known work 

 of the late Dr. Neumayr 2 has, in the opinion of many geologists, established 

 the existence of climatic zones whose boundaries ran practically parallel 

 with the equator in Jurassic and Cretaceous times, and the possible 

 existence of similar climatic zones in Palaeozoic times has been elsewhere 

 suggested ; but it is very desirable that much more work should be done 

 on this subject, and it can only be carried out by paying close attention to 

 the vertical and lateral distribution of organisms in the stratified rocks. 



So far we have chiefly considered the importance of stratigraphical 

 geology in connection with the inorganic side of nature. We now come to 

 the bearing of detailed stratigraphical work upon questions concerning 

 the life of the globe, and here the evidence furnished by the geologist 

 particularly appeals to the general educated public as well as to students 

 of other sciences. 



Attention has just been directed to the probable importance of former 

 climatic changes in determining the distribution of organisms ; but the 

 whole subject of the geographical distribution of organisms during 

 former geological periods, though it has already received a considerable 

 amount of attention, will doubtless have much further light thrown upon 

 it as the result of careful observations carried out amongst the stratified 

 rocks. 



So long ago as 1853, Pictet laid it down as a palaeontological law that 

 "the geographical distribution of species found in the strata was more 

 extended thau the range of species of existing faunas." One would 

 naturally expect that at a time when the diversity of animal organization 

 was not so great as it now is, the species, having fewer enemies with 

 which to cope, and on the whole not too complex organizations to be 

 affected by outward circumstances, would spread further laterally than 

 they now do ; but as we know that in earliest Cambrian times the 

 diversity of organization was very considerable, it is doubtful whether 

 any appreciable difference would be exerted upon lateral distribution 

 then and now, owing to this cause. At the time at which Pictet wrote, 

 the rich fauna of the deeper parts of the oceans, with its many widely 

 distributed forms of life, was unknown, and the range in space of early 

 organisms must have then struck everyone who thought upon the subject 



1 J. W. Gray and P. F. Kendall, " The Cause of an Ice Age ": Brit. Assoc. Rep. 

 (1892), p. 708. . ,, 



- M. Neumayr, " Ueber kliinalische Zonen wiihrend der Jura- und Kreidezeit : 

 Denkschr. der math -naturwissen. Classe der k. k. Akad. der Wissenscliafteii, 

 vol. xlvii. Vienna, 188o. 



