i 8. GEOLOGY OF ENGLAND. 207 



2. Lava, Scoria?, Pumice, Ashes, &c. : — products of 

 modern dormant and active sub-aerial volcanoes. 



Observations. — In this class are placed the mineral productions of 

 fire, or subterranean heat, ejected from beneath the surface, through 

 fissures or rents, whether in ancient or modern times. These igneous 

 materials are of all ages ; they traverse alike the hypogene rocks, and 

 the sedimentary strata, as well as the most recent deposits. 



Secondary. 



6 5 4 3 2 



Lign. 32.* — Diagram of the relative position of the rocks 



and strata in england. 



1. Tertiary strata. 2. Secondary. 3. Palaeozoic. 4. Older Palaeozoic. 



5. Metamorphlc rocks. 6. Plutonic (granitic) rocks. 



8. Geology of England. — By an inspection of the 

 Geological Map of England, Plate L, it will be seen that 

 the principal formations successively appear on the surface, 

 somewhat in their true chronological order {Lign. 32*), as we 

 pass from the eastern or south-eastern part of the Island to 

 the west or north-west ; as, for example, from the coast of 

 Suffolk to Cardigan Bay, or from London to Liverpool. 

 Thus, the Tertiary deposits are spread along the eastern 

 and south-eastern maritime districts ; and in proceeding in 

 a north-westerly direction, we successively travel over the 

 Cretaceous, Oolitic, Triassic, Carboniferous, Devonian, 

 Silurian, and Cambrian systems ; and, lastly, metamorphic 

 and primary rocks appear. 



This distribution of the strata has imparted a peculiar 

 character to the physical geography of England. The 

 Alpine or mountainous districts, which extend north and 

 south along the western portion of England and Wales, 

 from Cornwall to Cumberland, are formed by the elevated 



