RELATION OF BIOLOGY to GEOLOGICAL INVESTIGATION 26*3 



tion of tbe fossil Protozoa has precisely tbe same basis as lias that of 

 the living forms. 



The classification of fossil plants is, in a general way, similar to that 

 of living plants, and so far as the recognition of the great classes and 

 subclasses is concerned it is the same — thai is, each of these higher 

 divisions of the vegetable kingdom is recognizable among fossil-plant 

 remains by its peculiar histological structure and the characteristic 

 plan of its foliage venation ; but the method of discrimination of species 

 and genera of fossil plants is wholly different from that which is em- 

 ployed in the study of living plants, the latter method being impractica- 

 ble because of the imperfection of the fossil material. In the case of 

 living plants the detailed structure of the flower and fruit together 

 with the general structure of the whole plant forms the basis of classi- 

 fication. In the case of fossil plants, however, classification is based 

 almost wholly upon foliage, the main reliance for the discrimination of 

 species being upon the venation of leaves the imprints of which are 

 found upon the riven surfaces of stratified rocks, while their form or 

 marginal outline is the principal reliance for the discrimination of 

 genera. Other data are sometimes used for classification, such as the 

 general form of the plant so far as it may be determinable, the micro- 

 scopic woody structure, etc.; but these are rarely available and are 

 generally less satisfactory than arc those which are furnished by foliage. 



In presenting the foregoing statements concerning the character of 

 fossil remains I have taken occasion to indicate their high biological 

 value not only when considered as fossils, but even in comparison with 

 living forms as a standard, especially when studies and comparisons of 

 them are made with reference to the principles of comparative anatomy; 

 and I have also asserted their paramount value in geological investiga- 

 tions. Still, I have not hesitated to call attention to their imperfection 

 and their faunal and floral incompleteness — that is, I have thought it 

 necessary to indicate how incompletely any of the faunas and floras 

 which have formerly existed upon the earth are, or can be, represented 

 by them, and also how imperfect, even as fossils, are a majority of the 

 specimens which reach the geologist's hands. My object in doing this 

 is to show that the boundaries of possible knowledge with reference to 

 the life which has formerly existed upon the earth lie within the limit 

 which some authors have seemed disposed to assign to it, and in the 

 same connection I have called attention to certain other facts wheh in- 

 dicate that at least portions of the knowledge which is legitimately at- 

 tainable may be overestimated or misapplied. 



This treatment of the subject would be unfair if it were not accom- 

 panied by statements of facts and principles showing the paramount 

 importance of fossil remains in the prosecution of geological investi- 

 gation. Such a showing will be made in the Following essays, and in the 

 same connection the true value and teaching of fossils will also be dis- 

 cussed. 



