Chap. X. THROUGHOUT THE WORLD. 327 



forms dominant in the highest degree, wherever pro- 

 duced, would tend everywhere to prevail. As they pre- 

 vailed, they would cause the extinction of other and 

 inferior forms ; and as these inferior forms would be 

 allied in groups by inheritance, whole groups would 

 tend slowly to disappear ; though here and there a 

 single member might long be enabled to survive. 



Thus, as it seems to me, the parallel, and, taken in a 

 large sense, simultaneous, succession of the same forms 

 of life throughout the world, accords well with the prin- 

 ciple of new species having been formed by dominant 

 species spreading widely and varying ; the new species 

 thus produced being themselves dominant owing to in- 

 heritance, and to having already had some advantage 

 over their parents or over other species ; these again 

 spreading, varying, and producing new species. The 

 forms which are beaten and which yield their places to 

 the new and victorious forms, will generally be allied in 

 groups, from inheriting some inferiority in common ; 

 and therefore as new and improved groups spread 

 throughout the world, old groups will disappear from 

 the world ; and the succession of forms in both ways 

 will everywhere tend to correspond. 



There is one other remark connected with this subject 

 worth making. I have given my reasons for believ- 

 ing that all our greater fossiliferous formations were 

 deposited during periods of subsidence ; and that 

 blank intervals of vast duration occurred during the 

 periods when the bed of the sea was either station- 

 ary or rising, and likewise when sediment was not 

 thrown down quickly enough to embed and preserve 

 organic remains. During these long and blank inter- 

 vals I suppose that the inhabitants of each region 

 underwent a considerable amount of modification and 

 extinction, and that there was much migration from 



