300 FORMS OF LIFE CHANGING. [Chap. XI. 



of parallelism in the succession of the productions of the land than 

 with those of the sea. 



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 principle 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 spreading, varying, and pro- 

 ducing 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 

 therefore, 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 embed and preserve organic 

 remains. During these long and blank intervals I suppose that the 

 inhabitants of each region underwent a considerable amount of 

 modification and extinction, 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 is probable that 

 strictly contemporaneous formations have often been accumulated 

 over very wide spaces in the same quarter of the world ; but we are 

 very far from having any right to conclude that this has invariably 

 been the case, and that large areas have invariably been affected by 

 the same movements. When two formations have been deposited 

 in two regions during nearly, but not exactly, the same period, we 

 should find in both, from the causes explained in the foregoing 

 paragraphs, the same general succession in the forms of life ; but 

 the species would not exactly correspond ; fcr there will have been 

 a little more time in the one region than in the other for modifica- 

 tion, extinction, and immigration. 



I suspect that cases of this nature occur in Europe. Mr. 

 Prestwich, in his admirable Memoirs on the eocene deposits of 

 England and France, is able to draw a close general parallelism 

 between the successive stages in the two countries ; but when he 



