l«98j iV^'IF SCHEME OF GEOLOGICAL ARRANGEMENT 165 



neighbouring seas ; while others point to tropical or semi-tropical con- 

 ditions now only existing in latitudes where the dredge has only been 

 ■applied in most perfunctory ways. The method employed is also 

 largely dependent on the personal equation of observers who, un- 

 fortunately, have been separated by our ridiculous theories into 

 separate schools of students, one school dealing with recent and 

 another with fossil molluscs, as if either could possibly be studied 

 satisfactorily without continual reference to the other. The conse- 

 quence has been the creation of a number of fossil species which 

 had already been described and named as recent. Lyell was him- 

 self aware of some of his own difficulties. Thus, in 18.36, he calls 

 attention to the discrepancy in the results obtained by Deshayes 

 and Dr Beck, when they examined the proportion of living to extinct 

 forms among the crag shells, ]Jr Beck going the length of saying 

 that, although a larger proportion of shells in the crag approach 

 very near to others which now live in our northern seas, he regarded 

 them as almost all of distinct species and unknown as living. Lyell 

 adds the pertinent sentence. " In regard to the discordance in the 

 results at which these eminent conchologists have arrived, it may 

 arise, not only from the une(|ual opportunities which they have 

 enjoyed of examining the necessary data, but also in part to the 

 different estimate which tliey have formed of the amount of varia- 

 tion necessary to constitute a distinct species. One instance," he 

 says, " will sufficiently illustrate my meaning. Those naturalists 

 who agree with M. Deshayes in referring all the living varieties 

 of Lucina dAvarieata brought from different countries to one and the 

 same species, will identify many more fossils with recent shells than 

 those who agree with Dr Beck in dividmg the same recent individuals 

 of Lucina divaricata into six or eight distinct species" (Proc. Gcol. Soc. 

 ii. 372-3). Again, according to our modern lights, the proportion 

 of extinct to recent forms in a particular place may be largely acci- 

 dental, a shift of the sea bottom might divert the Gulf Stream, or 

 the corresponding cold Newfoundland current, and utterly change 

 the moUuscan fauna of a particular district, and yet be only a local 

 and adventitious fact. 



The only virtue of the criterion in question, if it has one at all, 

 is that it is of universal and not of mere local application. We can, 

 no doubt, count the shells in a New Zealand bed as we can in a crag 

 bed, and we can then compare the proportions of living to extinct 

 forms in them both, and thus establish a common measure, but 

 the common measure is an utterly misleading and absurd one. The 

 geological history and conditions of the two life-provinces are so 

 <Iifferent that no rational conclusion can be derived from the fact 

 that two beds at the antipodes to each other happen at a particular 

 moment to contain the same number of recent forms. The recent 



