TRANSITION SERIES. 55 



CHAPTER VII. 



Strata of the Transition Series. 



Thus far we have been occupied with rocks, in which we 

 trace chiefly the resuhs of chemical and mechanical forces ; 

 but, as soon as we enter on the examination of strata of the 

 Transition Series, the history of organic Kfe becomes asso- 

 ciated with that of mineral phenomena.* 



The mineral character of the transition formations pre- 

 sents alternations of slate and shale, with slaty sandstone, 

 limestone, and conglomerate rocks ; the latter bearing evi- 

 dence of the action of water in violent motion ; the former 

 showing, by their composition and structure, and by the 

 organic remaiiis which they frequently contain, that they 

 were for the most part deposited in the form of mud and 

 sand, at the bottom of the sea. 



Here, therefore, we enter on a new and no less curious 

 than important field of inquiry, and commence our exami- 

 nation of the relics of a former world, with a view to ascer- 

 tain how far the fossil members of the animal and vegetable 

 kingdoms may, or may not, be related to existing genera 

 and species, as parts of one great system of creation, all 

 bearing marks of derivation from a common author.f 



* It is most convenient to include within the Transition series, all 

 l.inds of stratified rocks, from liie earliest slates, in which \vc find the 

 first traces of animal or vegetable remains, to the termination of the great 

 coal formation. The animal remains in llic more ancient portion of this 

 scries, viz. the Grauwacke group, though nearly allied in genera, usually 

 differ in species from those in its more recent portion, viz. the Carboniferous 

 group. 



t In Plate 1, I have attempted to convey some idea of the organic re- 



