Il] FOSSIL PLANTS AND DISTRIBUTION. 15 



in their relations to the superposition and relative age of the 

 sedimentary formations^" 



To turn for a moment to some of the most obvious con- 

 nections between palaeobotany and the wider sciences of botany 

 and geology. The records of fossil species must occupy a 

 prominent position in the data by which we may hope to solve 

 some at least of the problems of plant evolution. From the 

 point of view of distribution, palaeobotany is of considerable 

 value, not only to the student of geographical botany, but to 

 the geologist, who endeavours to map out the positions of 

 ancient continents with the help of palaeontological evidence. 

 The present distribution of plants and animals represents but 

 one chapter in the history of life on the Earth ; and to under- 

 stand or appreciate the facts which it records, we have to look 

 back through such pages as have been deciphered in the earlier 

 chapters of the volume. The distribution of fossil plants lies 

 at the foundation of the principles of the present grouping of 

 floras on the Earth's surface. Those who have confined their study 

 of distribution to the plant geography of the present age, must 

 supplement their investigations by reference to the work of 

 palaeobotanical writers. If the lists of plant species drawn up 

 by specialists in fossil botany, have been prepared with a due 

 sense of the important conclusions which botanists may draw 

 from them from the standpoint of distribution, they will be 

 readily accepted as sound links in the chain of evidence. 

 Unfortunately, however, if many of the lists of ancient floras 

 were made use of in such investigations, the conclusions arrived 

 at would frequently be of little value on account of the un- 

 trustworthy determinations of many of the species. In the case 

 of particular genera the study of the distribution of the former 

 species both in time and space, that is geologically and geo- 

 graphically, points to rational explanations of, or gives added 

 significance to, the facts of present day distribution. That 

 isolated conifer, Ginkgo biloba L. now restricted to Japan 

 and China, was in former times abundant in Europe and 

 in other parts of the world. It is clearly an exceedingly ancient 

 type, isolated not only in geographical distribution but in 

 1 Humboldt (48), vol. i. p. 274. 



