GEOLOGICAL PALAEONTOLOGY Si 



animals necessarily selected the same kind of surround- 

 ings as those favoured by their descendants, reliance can 

 usually be placed on adaptive morphological features. 

 The latter basis for argument has a further advantage, 

 since it can be recognized in entirely extinct forms. 

 There is still room for doubt as to the precise systematic 

 position of the Tabulate " Corals " ; but the correspond- 

 ence of their general structure with that of living 

 Madreporaria makes similarity of habitat more than 

 probable. Again, the true Coelenterate affinities of the 

 Graptolites are not securely established, but there can 

 be no reasonable hesitation in ascribing to these extinct 

 animals habits of life like those adopted by recent 

 Hydrozoa and Polyzoa possessing comparable morpho- 

 ogical features. 



Just as some living Invertebrate types are known to 

 be capable of maintaining vitality under a variety of 

 conditions, or in spite of relatively sudden changes of en- 

 vironment, so some kinds of fossils may not imply definite 

 physiographical qualities for the stratum in which they 

 occur. As a general rule, the more highly specialized 

 groups are sensitive to change ; simpler types are more 

 adaptable. The Distinction applies equally in human 

 affairs : a general education enables its survivor to lay 

 his hand to almost any available work, the specialist is 

 incapable of success beyond his particular sphere. 



Lastly, it must be remembered that the relics of 

 organisms may often be drifted into very different 

 physiographical provinces from those essential for the 

 life of their owners, and may become embedded in in- 

 appropriate matrices among strange companions. The 

 frequent occurrence of fossil-wood in the Forest Marble 

 and Lower Greensand could never be used as evidence 

 that Conifers once grew in oyster-beds ; similarly the 

 presence of fresh-water shells mingled with those of 

 6 



