THE LOWER SILURIAN PERIOD. 



95 



h 

 $ 



GENERALIZED SECTION OF THE LOWER SILURIAN ROCKS 

 OF WALES. 



Fig. 34- 

 . ........... ...... ' f May Hill Sandstone 



'''-'"^^J'*-*--' '--I" 1 (baseofUpper Silu- 

 ^^s^S^^^- ( rian). 



O 



o 



Llandovery Group. 



Upper Bala. 



Lower Bala. 



Upper Llandeilo. 



....... Middle Llandeilo. 



...... Lower Llandeilo. 



Upper Arenig. 



., Middle Arenig. 



Lower Arenig (Up- 

 per Tremadoc 

 Group). 



Tremadoc Slates 

 (Lower Tremadoc 

 Group). 



In North America, both in the 'United States and in Can- 

 ada, the Silurian rocks are very largely developed, and may be 

 regarded as constituting an exceedingly full and typical series 



