372 L. F. Ward — Fossil Dicotyledonous Leaves. 



genera. In many cases they have done this for Eocene, and 

 even for Cretaceous fossils, where the form and nervation 

 seemed to justify it. In Heer's arctic work this was sometimes 

 done from incomplete fragments, and there are cases in which 

 this has been afterward confirmed by the discovery of more 

 complete material. 



But carefully as the laws of nervation have been worked out 

 and laid down in systems, there is no one who does not feel 

 that we are indebted more to the extraordinary skill and pene- 

 tration of the authors of these systems in reaching correct con- 

 clusions through their intuitive perceptions than we are to any 

 power which such rules unaided by such perceptions can give 

 to reach reliable results. Moreover, the investigator who above 

 all others possessed this intuitive instinct, Professor Oswald 

 Heer, is no longer in the field, others who so successfully 

 labored with him have reached an advanced age and must ere 

 long cease their labors, while younger men are springing up in 

 many lands to take up and continue a work which seems as 

 yet to have been only just begun. 



In such a field, from which if properly cultivated such rich 

 harvests may be expected for science, which yet depends so 

 largely upon the personal qualities of the investigator, it be- 

 comes of the utmost importance that sound and safe methods 

 be adopted, and that if any unsound or unsafe methods have 

 been employed, as it may well be expected that there have 

 been during the early history of the science, they be revised or 

 rejected and new and better ones introduced. 



It is doubtless with a keen sense of this truth that Dr. A. Gr. 

 Nathorst of Stockholm, upon whom Heer's mantle seems to 

 have fallen, at least so far as the arctic fossil floras are con- 

 cerned, in a very recent paper in the " Botanisches Central- 

 blatt " (Band xxvi, 1886) lifts up a warning voice. It is not 

 the first time that he has called a halt in the too rapid and con- 

 fident march of paleontology. The great commotion which he 

 so recently produced in the Silurian waters has as yet scarcely 

 ceased, and this paper seems likely to create an almost equal 

 disturbance in those of the Cretaceous and Tertiary. 



Dr. Nathorst considers that in referring fossil leaves, where 

 other organs are not known, to living genera vegetable paleon- 

 tologists are in danger of claiming too much, and that the older 

 the formation in which they are found the greater this danger 

 is. He thinks that for Cretaceous species, such as those from 

 the Cenomanian beds of Greenland and of Bohemia and from 

 the Dakota group of the United States, such reference is 

 wholly unjustifiable ; and even for Eocene and Miocene plants 

 he says that the material must be abundant and in an excel- 

 lent state of preservation to warrant this course. He believes 



