RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. .'JOT 



By referring to the table on Plate xiv it will be seen that the time 

 range of none of the nonmarine kinds of fossil remains extends much 

 beyond the estimated later half of geological time, and that the range 

 of a part of them is nnicli less. It will also be observed that the time 

 range of marine invertebrates is from the beginning to the end of the 

 time represented by the geological scale. Therefore, there is no possi- 

 bility of making comparisons between remains of marine animals and 

 those of all other animals as well as those of land plants for a very 

 large early part of the geological scale, because none of the latter kinds 

 have been discovered there. Indeed, opportunities for any such com- 

 parisons for the whole Paleozoic portion of the scale, besides those 

 which are practicable between remains of the marine animals and those 

 of the land plants of the Carboniferous system, are very few and com- 

 paratively unimportant. It is probable that many and important non- 

 marine deposits were formed during Paleozoic time and that they con- 

 tained the remains of nonmarine faunas, but reference is here made 

 only to the present extent of our knowledge in that direction. 



For the Mesozoic and Cenozoic portions of the geological scale oppor- 

 tunities are much more numerous for comparing fossil remains of ma- 

 rine with those of nonmarine origin than they are for the Paleozoic 

 portion. This is because nonmarine formations are of more frequent 

 occurrence among the sedimentary rocks of the two later eras than 

 among those of Paleozoic era, and also because of the greater abun- 

 dance and variety of the remains of nonmarine and land faunas and of 

 laud floras in those later formations. It is, however, a fact of great 

 importance in this connection that the aggregate proportion of non- 

 marine formations to those of marine origin, even for the Mesozoic and 

 Cenozoic portions of the scale, is very small. 



It is thus apparent that for the Paleozoic portion of the scale it is 

 marine formations almost exclusively with which the geologist has to 

 deal, and that for the remainder of the scale marine formations are far 

 in excess of the nonmarine. Indeed, they are so far in excess that, 

 with the exception of a few regions like the interior portion of North 

 America, for example, the occurrence of nonmarine formations is quite 

 exceptional. 



The absence of marine deposits among the formations of the earlier 



part of the geological scale and the great excess of the mari >ver 



the nonmarine among those of the later part, even where the latter 

 are most abundant, is a great impediment to the comparisons which it 

 isdesirable to make between them aud their fossil contents respectively. 

 Still, this is not a greater impediment to such comparisons than is the 

 incongruity or want of reciprocal relation not only between the marine 

 and nonmarine, but between the different kinds of the latter.* 



*Dr. Theodore (Jill lias clearly pointed out the incongruity between land and 

 marine faunas from the standpoint of recent biology. See Proc. Biolog. Sue, Wash- 

 ington. Vol. 2, p. 32. lXX->; ami Tin- Nation. Vol. 1' 1 . \>. 13. 1877. 



