32 



GEOLOGICAL MEMOIRS. 



C. 



I. CarboniferotjsPeriod -{ e. 



9- 



Sandstone 



(Zech- 



by letters, and the different zones in them by numbers attached. 

 The six remaining eohimns are appropriated to the various forma- 

 tions, of which he adopts the following periods and subdivisions : — 



a. Lower Silurian. 



b. Upper Silurian. 

 Devonian. 



Mountain limestone. 

 Coal formation. 

 Lower New Red 



{Todtliegende). 

 Magnesian limestone 



stein) . 

 St. Cassian beds. 

 Bunter or Variegated sandstone. 

 Muschelkalk. 

 Keuper, or Upper New Red 



Sandstone. 

 Lias. 



Lower Jurassic. 

 Upper Jurassic. 

 Wealden. 

 Neocomian. 

 Greensand. 

 Chalk. 



Nummulite formation. 

 Lower Tertiary. 

 Middle Tertiary. 

 (Molasse.) 

 Upper Tertiary. 

 Diluvial. 

 Alluvial. 

 Living. 



IL Trias or Salt Period. \ 



IIL Oolitic Period 



IV. Cretaceous Period 



V. Tertiary or Molasse<J 

 Period. I 



m. 



VL Recent Period 





S'ome of these divisions do not represent formations chronologi- 

 cally distinct, but are introduced only provisionally from uncertainty 

 as to the true position of the beds included in them. Others again 

 should probably be further divided, though the want of precision in 

 the nomenclature and divisions of various authors renders this at 

 present impossible. Thus the St. Cassian beds, h, are kept separate 

 until it is determined whether they form a distinct chronological 

 formation between the Zechstein and Muschelkalk, and hence pro- 

 bably better following ^, or are merely a peculiar facies of the Mu- 

 schelkalk. In the oolitic series no further subdivision between the 

 lias and the Kimmeridge clay could be effected ; and though it was at 

 first attempted to place a limit between the Oxford clay and the 

 coral rag, this had subsequently to be given up from the multitude 

 of common species. The Wealden is kept separate, some geologists 

 regarding it as only the lacustrine aspect of the Neocomian. In the 

 latter, q, the lower greensand of Dr. Fitton is included, but his green- 

 sand from Blackdown is united with the greensand r. This forma- 



