678 JAMES PERRIN SMITH 



France, and England, and by means of them was able to bring 

 into harmony the local subdivisions already established in these 

 various countries. 



This was an important step in the right direction, but experi- 

 ence has shown, since Oppel's time, that these zones were not 

 universal, and could seldom be recognized outside of the province 

 where they were established — not even there always, when there 

 was much difference of facies. So this scheme failed of its 

 immediate purpose, although the final results of it have been 

 more important than Oppel probably ever anticipated. 



A further application and enlargement of Oppel's plan has 

 been attempted by Buckman, 1 who has divided the Jurassic for- 

 mation into hemerae, based on the occurrence of certain charac- 

 teristic species of ammonites. An hemera represents a time con- 

 siderably shorter than a zone, for the Lias, or Lower Jura, alone 

 is divided into twenty-six hemerae. These are undoubtedly of 

 much use to the stratigraphic paleontologist in England, prob- 

 ably in France, and possibly in Germany; but these hemerae can 

 not possibly be identified away from the limited province where 

 they were established, for in the Alpine or the Austrian Jura one 

 is often lucky to be able to tell whether certain beds belong to 

 Lower, Middle, or Upper Jura. Such finely drawn subdivision 

 is of use only in local stratigraphy. 



Buckman further classed a number of he?nerae together in 

 ages, based on the development of a group or series of species ; 

 in the Lias alone there are four of these ages, which correspond 

 more nearly to the zones of Oppel, but even these could hardly 

 be recognized in southern Europe, and much less in Asia or 

 America. 



Oppel thought that his zones were universal, or interregional, 

 but only occasionally can one of them be identified outside of 

 the province where it was named. This is due to the distribu- 

 tion of certain characteristic fossils outside of their usual range, 

 on account of conditions temporarily facilitating interregional 



'Quart. Jour. Geol. Soc. London. Vol. LIV, 1898. On the Grouping of some 

 Divisions of so-called Jurassic Time. 



