CHAPTER III. 



THE IMPERFECTION OF THE GEOLOGICAL 

 RECORD. 



/^ OMPLAINTS of the imperfection of the geological 

 v_/ record are rife among those biologists who expect to 

 find continuous series of fossils representing the gradual trans- 

 mutation of species. No doubt these gaps are in some cases 

 portentous, and unfortunately they often occur just where it is 

 most essential to certain general conclusions that they should 

 be filled up. Instead, however, of making vague lamentations 

 on the subject, it is well to inquire to what causes these gaps 

 may be due, to what extent they invalidate the completeness 

 of geological history for scientific purposes, and how they may 

 best be filled. 



Here we may first remark that it is not so much the physical 

 record of geology that is imperfect as the organic record. Ever 

 since the time of Hutton and Playfair we have learned that 

 the processes of mineral detrition and deposition are contin- 

 uous, and have been so throughout geological time. The 

 erosion of the land is constantly going on, every shower carries 

 its tribute of earthy matter toward the sea, and every wave 

 that strikes against a beach or cliff does some work toward 

 the grinding of shells, pebbles or stone. Thus, everywhere 

 around our continents there is a continuous deposition of beds 

 of earthy matter, and it is this which, when elevated into new 

 land, has given us our chronological series of geological forma- 

 tions. True, the elevating process is not continuous, but, so 



