40 COSMIC PHIL0S0PH7. [pt. u. 



elevation when archipelagos are being converted into con- 

 tinents, and when shallow parts of the sea, hitherto divided 

 by deep channels, are getting practically united together by 

 the diminishing depth of the channel. During such periods 

 it is not only the inorganic agencies of climate and soil 

 which will be altered ; the organic environment of each 

 group of organisms will be immensely increased in extent 

 and heterogeneity. The struggle for existence will increase 

 in violence, and there will be an increased amount both of 

 variation and of extinction. 



We are thus driven to the remarkable conclusion, not only 

 that each system of fossiliferous strata now remaining has 

 been preceded and followed by systems destroyed as fast as 

 they were formed, but also that the systems thus destroyed 

 coincided with the pe'riods which must have been richest in 

 transitional forms. 



But notwithstanding the extreme imperfection of the geolo- 

 gical record, and notwithstanding these special difficulties in 

 the way of finding transitional forms, such forms are frequently 

 met with. Indeed it may be asserted, as one of the most 

 significant truths of palseontology, that extinct forms are 

 almost always intercalary between forms now existing. Not 

 only species, genera, and families, but even orders of con- 

 temporary animals, apparently quite distinct, are now and 

 then fused together by the discovery of extinct intermediate 

 forms. In Cuvier's time, horse, tapir, pig, and rhinoceros 

 were ranked as a distinct order from cow, sheep, deer, buffalo, 

 and camel. But so many transitional forms have been found 

 in tertiary strata that pachyderms and ruminants are now 

 united in a single order. By numerous connecting links the 

 pig is now seen to be closely united with the camel and 

 the antelope. Similar results relating to the proboscidians, 

 the hysena family of carnivora, the apes, the horse, and the 

 rhinoceros, have been obtained from the exploration of a 

 single locality near Mount Pentelikos in Greece. Among 



