ANNIVERSARY ADDRESS OF THE PRESIDENT. U 



The question has great weight ; but I do not see that it is likely 

 soon to be solved, chiefly for want of a sufficient amount of precise 

 data. The most analogous case that occurs to me at present is that 

 of the Drift ; for there is reason to believe that all, or nearly all, the 

 Molluscan life that immediately preceded the deposition of the glacial 

 strata has survived very extensive physical operations which involved 

 remarkable changes of climate, accompanied by deep submergence 

 and re-elevation of enormous areas. Both in this case and in that 

 of the Oolitic and Cretaceous strata formerly cited, one of the elements 

 of the question involves great elevation and depression of wide areas, 

 and therefore serious changes of conditions. In the older one there is 

 no proof of any change of climatal conditions, and yet the change of life 

 is complete; and in the latter there is the strongest evidence of 

 extreme variation of climate without extinction of Molluscan species. 

 Sufficient time to promote the change was perhaps present in the 

 first case, and wanting in the second. 



Contemporaneity of Strata. — I now come to another question con- 

 nected with physical breaks. 



It is stated that over wide European and other areas, even as 

 far off as North America, the same kind of physical breaks occur as 

 in the British Islands, and sometimes at what are considered to be 

 the same points in the geological scale. The question has therefore 

 often been raised (I have already adverted to it), Are we justified in 

 considering formations to be altogether or approximately contem- 

 poraneous that contain the same general assemblages of fossils in 

 areas wide apart? 



The answer has sometimes been given in the negative, on the 

 minor ground that the two ends of the same bed are not necessarily 

 precisely contemporaneous, and on the larger issue that the existence 

 of the same species in strata far apart proves that they are not of the 

 same age, because it would take a long time for species that origin- 

 ated in one area to travel into another. The minor point presents 

 no serious difficulty ; but the larger one, which is an extension of the 

 same line of argument, is more difficult to dispose of. 



It appears to me, however, that such reasoning is in error simply be- 

 cause the reasoner is apt unintentionally to consider a whole formation, 

 perhaps from 1000 to 7000 feet thick (as in the case of the Bala beds 

 and the Hudson River group), as if it were a bed or a thin set of beds 

 representing a particular sea-bottom at a particular time, whereas the 

 Bala beds represent a great many thousands of sea-bottoms more or 

 less regularly piled on each other very slowly. The question must 

 therefore arise, in connexion with duration of species, whether under 

 any circumstances the possible time, for instance, that it might have 

 taken to transmit species from the English to the American area is 

 likely to be comparable to the amount of time represented by the 

 interval between the lowest and the highest Bala strata, or even of a 

 longer period ; for if formations commonly believed to be approxi- 

 mately contemporaneous are not so, then the process of transmission 

 of a group from one area to another might be prolonged indefinitely, 

 so that, as supposed hypothetically by Professor Huxley, a Silurian, a 



