112 THE ORIGIN OF SPECIES 



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 their 

 having had some advantage over their already dominant 

 parents, as well as over other species, and again spread- 

 ing, varying, and producing new forms. The old 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 there- 

 fore, as new and improved groups spread throughout 

 the world, old groups disappear from the world; and the 

 succession of forms everywhere tends to correspond both 

 in their first appearance and final disappearance. 



There is one other remark connected with this subject 

 worth making. I have given my reasons for believing 

 that most of our great formations, rich in fossils, were 

 deposited during periods of subsidence; and that blank 

 intervals of vast duration, as far as fossils are concerned, 

 occurred during the periods when the bed of the sea was 

 either stationary or rising, and likewise when sediment 

 was not thrown down quickly enough to imbed and pre- 

 serve organic remains. Daring these long and blank 

 intervals I suppose that the inhabitants of each region 

 underwent a considerable amount of modification and ex- 

 tinction, and that there was much migration from other 

 parts of the world. As we have reason to believe that 

 large areas are affected by the same movement, it ia 

 probable that strictly contemporaneous formations have 

 often been accumulated over very wide spaces in the 



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