TRANSITION FROM THE PALAEOZOIC TO THE MESOZOIC. 



411 



the Devonian, which is often called Old Eed sandstone. It is further 

 distinguished throughout, especially the upper part, by variegated shales, 

 and therefore called altogether Poikilitic group. It is also distin- 

 guished throughout by the presence of salt, and therefore called the 

 Saliferous group. Here, then, there were the strongest reasons for re- 

 garding the whole as one group, distinctly separated by unconformity 

 from the underlying Coal. The upper part of this continuous series 

 contained undoubted Mesozoic fossils. The line of unconformity was, 

 therefore, naturally believed to be the line between Palaeozoic and Meso- 

 zoic. Unfortunately, the lower portion is very barren of fossils, and 

 this means of correcting the stratigraphic conclusion was at first nearly 

 wanting. When fossils were discovered in sufficient numbers, how- 

 ever, they showed a greater alliance with the unconformable Coal below 

 than with the conformable strata above. Thus, if we make the division 

 between Palaeozoic and Mesozoic on stratigraphical grounds, we would 

 find it between the Coal and the overlying strata ; while, if we make it 

 on paleontological grounds, we would have to draw the line through 

 the midst of the conformable strata, a, giving one half to the Palaeozoic 

 and the other half to the Mesozoic. The lower Palaeozoic half is called 

 the Permian* 



As a broad general fact, therefore, the great commotion which is 

 called the Appalachian revolution took place, or commenced to take 

 place, at the end of the Coal period. But the fauna and flora were not 

 immediately extermi- 

 nated, but struggled on, 

 maintaining, as it were, 

 a painful existence un- 

 der changed conditions, 

 themselves meanwhile 

 changing, until complete 

 and permanent harmony 

 was re-established with 

 the opening of the Mes- 

 ozoic. If we may use an 

 illustration, the Appala- 

 chian revolution was the 

 death-sentence of Palae- 

 ozoic types, but the sentence was not instantly executed. This transi- 

 tion period, between the sentence and the execution of Palaeozoic types, 

 is the Permian. 



It is well here to draw attention to the fact of this great change of 



Fig. 589. 



Fig. 591. 



Figs. 588-592.— American Permian Fossils (after Meek): 588. 

 Euraicrotis Hawni. 589. Myalina Permiana. 590. Bake- 

 wellia parva. 591. Pleurophorus subcuneatus. 592. A Gas- 

 teropod. 



* In Germany it is closely allied stratigraphically with the Triassic, and therefore by 

 many put in the Mesozoic, and called Dyass. 



