RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 305 



which have been referred to the fishes. The shorter of the two lines in- 

 dicates the known range of the teliosl fishes and the longer which of 

 the other kinds, the latter including certain forms that differ materially 

 from any living fishes. 



The time range of Batrachians and reptiles, so far as it is known, is 

 shown by the three perpendicular lines in the table under the letter D, 

 that of the dinosaurs alone being represented by the shortest line of 

 the three. 



The known time range of birds is represented by the single line under 

 the letter E. It is here assumed that most, if not all, the fossil tracks 

 round in Triassic strata and formerly referred to birds are those of 

 dinosaurs. 



The two lines in the table under the letter F represent the known 

 time range of mammals, the longer line representing that of the non- 

 placental and the shorter that of the placental mammals. 



The known time range of land plants is represented by the two lines 

 under the letter (1. The shorter line represents the range of the dicoty- 

 ledons and palms and the longer one that of all other kinds. The alga' 

 and diatoms are omitted from the table as being of little or no impor- 

 tance in the comparisons and discussions which are to follow. 



The earlier portion of the time range for each of the kinds of animals 

 and plants as shown by the perpendicular lines in the table is naturally 

 more incompletely and indefinitely represented by fossil remains than 

 is the later portion, because of the smaller variety and greater rarity of 

 those earlier remains and also in most eases because of the increasing 

 difference in character from living forms which is observable from later 

 to earlier formations. In Nome cases, however, the early portion of the 

 time range as it is now known begins so suddenly and with forms of 

 such high biological rank as to make it evident that its real beginning 

 was mucn earlier than it nas yet been proved to be by actual discovery 

 of fossil remains. The last mentioned fact is of great importance in 

 many respects, buc n does not necessarily affect the question under 

 consideration, because all estimates of the relative chronological value 

 of fossil remains must be confined co the kinds already known, and the 

 application of such estimates must be confined to those portions of the 

 geological scale in the strata pertaining to which the remains are 

 known to occur. 



Although much the greater part of all the known fossil remains of 

 the earth are of marine origin, it is a significant fact that most of the 

 general kinds represented in the table are either of nonmarine or hind 

 origin. The extreme diversity o'l these conditions of habitat implies a 

 wide diversity of character and suggests a wide difference of values. 

 It is this diversity which makes it necessary to discuss the different 

 kinds of tossil remains with reference to both habitat and conditions 

 of preservation. 



H. Mis. 114, pt, 2 20 



