396 CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 
anomalies, and also makes clear the existence of two deserted 
cols at Wortley (560 feet) and Thurgoland (675 feet). These 
cols lie in the direction of the original course of the stream A, 
and are, I believe, relics of its channel. If this be so the relative 
Fig. 3. 
MAP SHOWING THE OUTLINE OF THE GEOLOGICAL STRUCTURE OF THE 
DON VALLEY. 
height of the cols shows that the stream A must have been tapped 
at Thurgoland first, and afterwards that a little torrent flowing 
into the Don at Wortley (E, Fig. 4, III.) must have cut back 
