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 
