6 THE GEOLOGICAL EVIDENCES 



side by side with these forms we still meet with 

 those of a lower grade of organization, while still 

 others, belonging to the earlier periods of the 

 earth's history, have completely dropped out. 



As a second proof of his position the geologist 

 would be compelled to show the lines along which 

 certain organic forms have developed ; to speak 

 more explicitly, he would be required to indi- 

 cate a number of transitional types intermediate 

 in their relations between forms otherwise appar- 

 ently far removed from one another. These 

 are the so-called " missing links." Furthermore, 

 these missing links must appear at definite geolo- 

 gical periods, and not promiscuously at all times 

 and places. This is practically the sum total of 

 the proof that would be required of the geologist, 

 and I believe that I shall be able during the course 

 of the evening to show to your entire satisfaction 

 that he can furnish this proof, and furnish it in a 

 most convincing manner. 



I have placed before you a chart representing the 

 different geological periods, beginning with the 



