24 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



effects of environment. Several lineages (" species series "), 

 which are single genetic lines, have now been carefully worked 

 out. It cannot be said that in the present state of knowledge 

 the evolution of lineages can be definitely correlated with chang- 

 ing environment as indicated by the sediments containing them. 

 Certain cases (e.g., the Micrasters of the Chalk* or the Ammo- 

 nites of the Lias) show an evolution unaccompanied by any 

 apparent change in sedimentation or, so far as we can judge, 

 of the environment that would be reflected in the character 

 of the sediment. f 



But in such cases where lineages show progressive change 

 in their constituent forms, and the sediments containing them 

 an apparent constancy of environmental factors, we cannot 

 yet assume that evolution has proceeded independently of 

 environment.! Alternatively, we must face the fact that our 

 knowledge of sediments, particularly of those characters which 

 should be indexes of environmental change, is far from sufficient. 

 Our obvious course is to study more intensively the conditions 

 of sedimentation at the present day, and to apply the results 

 of such work to the rocks of the past. 



In the present state of knowledge it would almost seem 

 that on the whole the environmental caus?s leading to minor 

 changes in development have left their record in the sediments, 

 but that the greater changes and the evolution of lineages 

 cannot be correlated with known variations in lithology. 



* A. W. Rowe, Quart. Joum. Geol. Soc, Vol. 55 (1899), p. 494. 



f Mr. S. S. Buckman, in his " Inferior Oolite Ammonites " (Monogr. 

 Pal. Soc, Supplement, p. xv. (1898), wrote : " It is a great mistake to 

 suppose that Ammonites were influenced by the character of the deposit, 

 though this error has been so widely taught that nearly every writer, myself 

 included, has argued as if it were a fact. When Dorset, Somerset, and 

 Gloucestershire are compared, it will be found that the same species lived 

 when the deposit was argillaceous, arenaceous, or calcareous, and flourished 

 equally well. Notably is this the case when the Middle Lias of Dorset and 

 of Somerset are compared ; or the Lias- Oolite deposits of Dorset, Somerset, 

 and Gloucestershire, and these again with the Continent." 



X In the case of organisms such as ammonites, evolution may have 

 taken place elsewhere, and migration have brought them into the position 

 in which tliev are now found. 



