610 ON THE AGES OF EI VEE-V ALLEYS IN LINCOLNSHIRE. 



It would appear, therefore, that there has been an uplift across 

 this ancient line of drainage in Postglacial lines, causing the 

 Witham to turn westward and take its present course ; and the in- 

 fluence of the same uplift, if continued further north, may have 

 contributed to divert the Trent from its original eastward course via 

 the Lincoln valley. 



Whether this, however, was the case or not, the diversion of the 

 Trent could not have been effected unless a course had been already 

 prepared for it by the action of streams in lowering the longitudinal 

 valley south of Gainsborough. In comparing the two instances I 

 described of the diversion of an older stream by the extension of a 

 longitudinal river-valley, the chief difference appears to be this : — In 

 the first case, that of the Steeping and Calceby Becks, it was the 

 upper tributaries of the latter which were diverted into the longi- 

 tudinal valley ; while in the second case it was the main stream of 

 the Trent which was so intercepted and diverted. 



I believe that the principles above enunciated and exemplified 

 will explain the courses of certain other English rivers, and purpose 

 recurring to the subject in a future paper. 



Discussion. 



Mr. Evans instanced the case of the Waveney and the Little Ouse 

 once flowing from different sources, but now from one near Lopham 

 Ford, the deposit of glacial clay in this instance also forming an 

 element in the case. 



