Paleozoic 



The Lithosphere 



IT, . Zechstein 



Penman . { Rothliegendes 



Coal Measures 

 Carboniferous . - Millstone Grit 



Carboniferous Limestone Series 

 Devonian and Old Red Sandstone 



Ludlow 

 Silurian . . . - Wenlock 



Llandovery 



'Bala 

 Ordovician . . - Llandeilo 



Arenig 



Cambrian 

 Archaean 



Gneisses, Schists, etc. 



The meaning of the names of the great groups has 

 already been explained, but those applied to the smaller 

 subdivisions are less systematic. Thus the names of 

 the various formations of the Cainozoic group depend 

 upon the proportion of recent to extinct genera. For 

 instance, Eocene, the dawn of recent ; Oligocene, few 

 recent ; Miocene, less recent (containing a minority of 

 living forms) ; Pliocene, more recent (containing a 

 majority of living forms) ; Pleistocene, most recent. 



In the Mesozoic the origins are more varied. Thus 

 Cretaceous means chalk-bearing, Jurassic refers to the 

 occurrence of the rocks in the Jura Mountains, and 

 Triassic indicates threefold in allusion to the marked 

 threefold division of the beds of this age in Germany. 



The names of the Palaeozoic formations are, with the 

 exception of the Carboniferous, derived from the districts 

 where their details were first worked out. Thus Permian 

 from the province of Perm in Russia ; Devonian from 

 the county of Devon ; Silurian and Ordovician from 

 the districts occupied respectively, at the time of the 

 Roman occupation, by two British tribes, the Silures 



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