CHAP. VI.] CARBONIFEROUS PERIOD. 101 



which lies to the north and east of the island barrier. 

 Now a reference to the map (Plate IV.) will show that this 

 area over which the red rocks occur is exactly that which 

 is most likely to have been converted into a lake or group 

 of lakes by a very slight geographical change. The sea 

 had probably always been shallow at the northern and 

 eastern ends of the central island, and a union of these to 

 the mainland would completely enclose the area in ques- 

 tion, isolating it from the other areas of deposition, and 

 converting it into such a shallow lacustrine basin as the 

 facts seem to indicate. Such appears to have been the 

 last stage in the Carboniferous geography of the British 

 area. 



