230 THE CHAIN OF LIFE. 



complete over all the continents, of the speedy culmination 

 and early decadence of many types, and of the unchanged 

 permanerce of others, must in the main be sustained. It is 

 not too much to say that to account for these facts tne evolu- 

 tionist must abandon the idea of gradual change, and adopt 

 that of " critical periods " when sudden changes occurred. The 

 history becomes inexplicable, unless with Mivart, Le Conte, and 

 Saporta, we admit " periods of rapid evolution " alternating 

 with others of stagnation or retrogression ; and if we admit 

 these, we practically fall back on the old idea of creation ; only 

 it may perhaps be " Creation by Law." 



Note. — Professor Marsh has recently announced, in the American 

 Journal of Science., the discovery of a second small Marsupial mammal in 

 the Juras-ic of the Rocky Mountains, where it would seem that animals of 

 this kind were contemporary with the great reptiles of the genus 

 Atlantosaurus. The species described by Marsh are nearly related to 

 those found in the Jurassic of England. This is another curious case of 

 the simultaneous appearance of new forms of life in distant places. 



