78 HISTORICAL PALAEONTOLOGY. 
GENERALISED SECTION OF THE CAMBRIAN ROCKS IN WALES. 
Arenig Group (Base of the 
Lower Silurian). 
Tremadoc Slates. 
2 
= Upper Lingula Flags. 
s) Heegte 
is Middle Lingula Flags. 
= | 
Lower Lingula Flags. 
Menevian Group. 
Z 
= 
ea 
q 
< 
©) 
a Longmynd or Harlech Group. 
3 
-| 
Pre-Cambrian Rocks, 
The above may be regarded as giving a typical series of the 
Cambrian Rocks in a typical locality ; but strata of Cambrian 
age are known in many other regions, of which it is only 
possible here to allude to a few of the most important. In 
Scandinavia occurs a well-developed series of Cambrian de- 
posits, representing both the lower and upper parts of the 
