CEETABSr EIVER-V ALLEYS IN LINCOLNSHIRE. 



597 



whatever extent these longitudinal valleys might proceed, none of 

 the waters coming down them could ever cross the lowest original 

 transverse valley that was formed by the little primary river ;" and 

 he points out that the river Blackwater has never crossed the 

 primary transverse channel which runs southward from Cappoquin 

 in "Waterford, and never could do so unless something happened to 

 cut a channel lower down the remainder of the longitudinal valley 

 to Dungarvan Bay, and deeper than the channel already cut down 

 to Toughal Bay. 



Fig. 1. — Diagram of a Stream intercepting earlier Transverse 

 Streams. 



To suppose the possibility of such a channel being formed, in any 

 case was entirely outside the scope of Jukes's argument ; but the sequel 

 will show that it is worth while considering this possibility, and 

 calculating the results which would follow from the development of 

 such a channel. 



Fig. 2. — Diagram of probable changes in the Valley of 

 the Blackwater. 



Suppose, therefore, that a small stream ran into Dungarvan Bay as 

 at S in fig. 2, and that while the valley of the Blackwater was ex- 

 tending itself westward from Cappoquin, the valley of the stream S 

 was also extending itself westward from the coast. It is clear that 



