[24 THE STORY OF THE EARTH. 



and back margins. Subsequently, in the Austrian 

 s, especially at Hallstadt on the north, and St, 

 Man on the south, the Upper Trias abounds in 



shells which are a remarkable mixture of th 

 which survive from the Primary period, such as 

 OrthoceraSy Goniatitcs, Euomphaltis, Murchi$onia y 



with the shells which are found in the overlying 

 •a, such as Ammonites , Belemnitis y Ncri\ 



fam'a, Cardita, Thecidium. Therefore the sepa- 

 ration in life between the Trias and the Permian, 

 although mo>t marked, is not so absolute as it 

 would have appeared to be if those Alpine deposits 

 had been unknown. And the occurrence of genera 

 which had characterised the primary strata, is the 

 more interesting because other examples occur of 

 similar survival of types of lift- from the primary 

 time, in the occurrence of the gen us Leptaena in 

 the Lias, and of Spirifera in the Lias and Power 



tes. Such occurrences prove- that the change 



in life was a local change, ami that the primary 



types became e\tim t gradually, 



than the Keuper is a series of beds in 

 the west Of England not more than ioo feet thick, 

 known as the Peuarth beds or Kinetic beds, from 



their great development in the Rhaetic Alps. They 

 ncluded in the Trias by many \\ riters. William 



Smith referred to them as the White Puis, which 



mpact limestone forming the top of the 

 series, in marked contrast to the Blue l 

 rhe W bite l ias has occasionally been 

 ibstitute \^x lithographic slate, winch 



it resembles in appearance. I >rajj<>n-llies, Cock- 



asshoppers, and other inse< pre- 



yed in I he White I .ias, 



plentiful in the underlying black 

 at i\\r base ol \\ inch is the Rhael 



