Apeil 22, 1898.] , 



SCIENGE. 



571 



Now, while we think of all evolution as the 

 result of some kind or other of Selection this 

 remains an enigma. But when we distinguish 

 between the two processes of Isolation and Se- 

 lection and assign to each its true function we 

 get at once the explanation of our difficulty. 

 Determinate Evolution is due to the combined 

 action of Isolation and Selection. Indetermi- 

 nate Evolution is due to the action of Isolation 

 alone. 



I think that Darwin had this distinction in 

 his mind when he said that Natural Selection 

 was the chief, but not the only, cause of the 

 origin of species. At any rate, it seems to me 

 to embody the whole truth, although Darwin's 

 attention was chiefly devoted to establishing 

 the cause of Determinate Evolution by, what I 

 hope we may still call, Natural Selection. 



F. W. HUTTON. 



Cheistchuech, New Zealand, March 1, 1898. 



MODERN STEATIGRAPHICAL NOMENCLATURE. 



One of the most noteworthy features con- 

 nected with every one of the various branches 

 of the rapidly expanding science of modern 

 geology is a widespread and oft-deplored 

 change in terminology. Old names are dis- 

 carded, the meanings of others are altered, and 

 a host of apparently useless new ones are pro- 

 posed. 



In no department has the coining of new 

 names gone on more vigorously than in strati- 

 graphical geology. The reason is to be found 

 partly in the naturally favorable conditions that 

 prevail in the field, but largely in the change 

 of base that this branch of science has under- 

 gone in late years. 



The fundamental conception of the geological 

 formation, whether large or small, whether a 

 great series or a single bed, is a sharply defined 

 ' geological unit ' instead of a vaguely bounded 

 ' group ' of layers. The former is now clearly 

 distinguished by strictly physical characters 

 that are inherently the direct outgrowth of the 

 actual conditions giving rise to the formations. 

 The latter have been too often based upon 

 trivial or accidental features that are relatively 

 unimportant as critical criteria, either in corre- 

 lation or classification. 



The principle underlying the recent change 



in the method of naming geological formations 

 gives to each striatigraphical unit, a special 

 geographical designation taken from some prom- 

 inent town, watercourse, or feature of relief, 

 within the boundaries of the formation and 

 where the latter is typically or unusually well 

 shown. As thus established, the formation is a 

 well-defined and independent unit, having a 

 definite position in space, and always an exact 

 relative place in the geological scale, no matter 

 how the latter may be changed afterwards or 

 what method of classification is followed. This 

 definite stratigraphical unit contrasts strangely 

 with the unwieldy, ill-defined and usually little 

 understood large ' group ' of the past, the very 

 name of which commonly indicated either a 

 lack of exact knowledge of itself, or a covering- 

 up of almost total ignorance regarding its real 

 aflSnities. 



To be sure, the nomenclature in the field of 

 geology has been greatly increased, even 

 enormously enlarged, by the introduction of 

 the plan. The former list of names numbered 

 only two or three score or so — names of the 

 smallest subdivisions that went to make up the 

 general geological column. The names of the 

 new list run up into the hundreds or even 

 thousands, are different in every region, and 

 additions are constantly being received. 



Against this copious multiplication of geolog- 

 ical names protests long and loud have gone 

 up these several years past. Still, from time to 

 time, the protestations continue to be uttered. 

 Curiously enough, the struggle, if such it might 

 be called, has been largely reduced to a clash 

 between the practical field geologists on the one 

 hand and on the other the laboratory workers, 

 those especially interested in some particular 

 and limited phase of geology, and the paleontolo- 

 gists who see, in the new scheme, their standard 

 classification scattered to the four corners of the 

 earth and their usefulness in the domains of 

 geology diminished. And the former have 

 manifestly won. 



When, a decade and a-half ago, various geo- 

 logical surveys in this country were established 

 or reorganized those intrusted with the work 

 soon found that if speedy and exact results 

 were to be secured — substantial data upon 

 which all other workers could easily build — 



