144 VICTOR E. SHELFORD. 



communities through emigration, death, immigration. ,nid tin- 

 modification of more* by external -timuli. 



\". ECOLOGICAL Succi n>\ AND Si CCESSION OF SPI n -. 



The difference bet \\een ecological and geological succrinn 

 were suggested in my preceding paper. \\V noted that eco- 

 logical succession deals with tin- succession of ecological types. 

 We noted also that geological succession N due-, in ihe main, to 

 the death of a given set of species and the evolution of new ones 

 throughout geological time. While this is true of the broader 

 aspects, in the more detailed cases and especially in dealing with 

 recent post-glacial fossils, the palaeontologist often encounters a 

 vertical succession of fossils which have been left behind by 

 the migrations of a succession of species over the locality of fo-- 

 silization (Warming, '09, p. 362, Adams, '05 and '09, Sharff, 07, 

 esp. Chap. IX. and citations) . Palaeontologists may also encounter 

 vertical succession of fossils in situations \vhere such succession 

 as we have been describing has taken place. 



i. Vertical Succession of Fossils. ^Steenstrup ('41) found from 

 the study of fossils in moors that one kind of vegetation suc- 

 ceeded another. Various other workers (Andersson, '97) have 

 found similar arrangements. In the case before us the fossiliza- 

 tion of species would give a vertical succession of fossils. 



Turning again to the diagram, we note that the skeletal parts 

 of any fish in the earliest stages indicated by hypothetical stage 

 B might have been preserved as fossils. The accumulations of 

 humus which lead up to stage I would have covered the fossils 

 of stage B, the fish of stage B would be present, if at all, as 

 fossils at the bottom of the pond. 



Likewise, the accumulations of humus which led to stage 5 

 covered those skeletal parts of the fish of stage I, and the fish 

 of stage I should be found as fossils overlying those of stage B 

 and underlying those of stage 5. Again, the accumulations of 

 humus which led up to stage 7 co\ i-n-d fossils which were present 

 and added at stage 5, and the fish preser\ed .1- fossils from sta-e 

 5 would lie above all those preserved as fo-^iU lKm the younj 

 stages and below those of stage 7. Ko-.-iU from stage 14 and the 

 intermediate stages would lie at the top of the Aeries and above 

 those of stage 7. 



