CHAP. VIII.] TEIASSIC PERIOD. 131 



size and very irregular shape was formed. We cannot say 

 exactly how this was, in the first instance, filled with water ; 

 it does not seem to have had any previous connection with 

 the open sea as the Dyassic lakes had, and as the modern 

 Caspian has had ; it was probably a freshwater lake, which 

 gradually became salt by the concentration of its waters, 

 like the Salt lakes of North America. It may be that the 

 outlet of the lake which previously existed in the south- 

 west of England was blocked by volcanic disturbances and 

 local upheaval, so that its waters gradually rose and over- 

 flowed the low barrier of Palaeozoic rocks which separated 

 them from the northern tracts. However this may be, it 

 is certain that in Upper Triassic times there was a large 

 space of water occupying the whole of central England, but 

 divided by the Pennine chain into two long gulfs or arms, 

 one of which spread to some distance east of Lincolnshire 

 and Yorkshire (see Plate VI.), and the other extended into 

 Cumberland and the north-east of Ireland. How much of 

 the Irish Sea was covered by this arm it is very difficult 

 to say, and the geography of this portion of the lake can 

 only at present be guessed at. 



Southward a gulf extended across what is now the Eng- 

 lish Channel, and terminated in Normandy, but the course 

 of that part of the shore-line which ran below the east of 

 England is uncertain, because of the doubt existing with 

 regard to the age of the red rocks beneath London (see 

 p. 123), but the line on the map (Plate VL) is drawn in 

 accordance with the more probable view. 



We may feel confident that there was still a large tract 

 of land on the east side of the lake, comparable in many 

 respects to that which lay to the westward ; we know that 

 it was composed of Carboniferous, Devonian, and Silurian 

 rocks similar to those of North Devon, Wales, and Shrop- 

 shire, and we may reasonably assume that it was a hilly 

 and rocky region such as Wales is now, and presented a 



