:286 PRESTON J SURFACE GEOLOGY NORTH OF GRANTHAM. 



These beds are a series of clays, sands, and limestones, of 

 various qualities, and as their prevalent dip is towards the south-east 

 at a very slight angle, we get the hard beds forming escarpments 

 facing more or less west, and gentle dip slopes towards the east, 

 whilst the softer beds form the level tracts between these hills ; so 

 that a traveller coming from the west across this district would 

 encounter steep inclines — as at Barrowby and Whipperstall Hills 

 and gentle slopes as he passed on eastwards after reaching the 

 highest point of the escarpment. 



It would be impossible to study the geology of this district 

 without taking some account of the river Witham. This river has 

 a most interesting history, many of its stages revealing themselves 

 by investigation of the rocks and land surfaces over which it has 

 passed in the formation of its valley. South of Grantham the river 

 valley is comparatively new, being cut through the limestone to the 

 Upper Lias Clay by a gradual recession of the spring heads. At 

 Grantham the valley is of a much greater age, having been formed 

 at a time when the principal springs lay to the south-west, rising in 

 the vicinity of Denton and Woolsthorpe, and forming the valley now 

 occupied by the Mowbeck, a stream which enters the Witham at the 

 north end of Grantham, and which is now but the ghost of its 

 former self. 



Grantham is practically built on the sands and gravels of this 

 ancient river valley, which lies on the eroded surface of Middle Lias 

 Clay (Zone of Ammonites capricornas). Passing through Grantham 

 the valley continues northwards as far as the gap in the cliff at 

 Honington, although the Witham leaves it and takes a westerly 

 course at Barkstone. The alluvial deposits of the old valley continue 

 eastwards through the Honington gap into the Fenland beyond. 

 The question naturally arises, How was this great gap in the Cliff 

 Escarpment formed? 



Now, in the interesting paper on the Lincoln Gap, read before 

 the Union at Lincoln by Mr. Burton, he there describes how rivers 

 running in a continuous course from higher to lower ground, will 

 cut through hard and soft strata alike until a general slope is 

 reached ; and this explanation is equally applicable to the 

 Honington Gap, There is no doubt it was cut at a time when 

 the Witham, or some other river, flowed from the west at a higher 

 level than the top of the present Cliff escarpments. And although 

 we may not be able to trace the exact period when the gap was 

 formed, there is very little doubt but that the present river, until 

 quite a recent geological date, ran along the old valley beyond 

 Barkstone, and through the gap on towards Sleaford and the Fen 



Naturalist, 



