GEOLOGY 



western half of it that allowed water to enter from without, appears to 

 have existed between Kilsby and Crick, and through this gap a portion 

 of the glacier water poured after reaching a certain level, and in it left a 

 deposit of sand continuous with the Hillmorton beds. We thus have a 

 simple explanation of the disastrous quicksand encountered near the south 

 end of Kilsby tunnel when the latter was made, of the enormous volume 

 of water pumped from it, and the remarkable way in which the trial 

 holes failed to detect it. 



Southward of the Kilsby tunnel gap the water appears to have been 

 disposed of partly to the westward, around the southern end of the Marl- 

 stone outlier on which Welton stands, towards Braunston, and so into 

 the Learn valley ; partly along the valley through which the L. & N. W. 

 Railway runs from Watford to Weedon (see map), and thence along the 

 channel previously referred to as extending from Heyford to Courteenhall, 

 and on into the low-lying land constituting the valley of the Ouse. This 

 old channel was, there is much reason for believing, a branch of the 

 Ouse, and not the Nene as the nearest stream to it now is. The sand 

 beds which we rely upon for identifying the course of flow are, between 

 Wilton and Daventry, about 40 feet thick under 10 feet of gravel, and 

 nearly the same at other places south of the Nene (see p. 23). 



Lower Glacial Deposits 



The sand beds (not including the overlying gravel) although formed 

 by water action antecedently to the period of complete glaciation of the 

 county, no doubt ultimately passed upwards into an earth and boulder- 

 laden ice, and by this ice, valleys at a higher level, and otherwise less 

 accessible to glacier flood water were gradually choked, and the general 

 surface of the ground covered. The infilling Boulder Clays, or dirty 

 gravels of certain pre-glacial valleys may be regarded as an imperfectly 

 washed residue of this first ice sheet, and are therefore Lower Glacial 

 deposits, but on the whole the previous presence of an extensive ice sheet 

 can only be inferred from the modified Drift to be considered next. 



Mid-glacial Gravels. Inter-glacial Period 



The first glaciation was followed by a comparatively long interval of 

 time during which a mild climate prevailed. The retreat of the ice, like 

 its advance, was accompanied by great floods, implying rather rapid 

 changes of climate. It would appear that subaerial melting produced 

 superglacial floods sufficient in intensity to carry away all the finer 

 argillaceous matter previously included in the ice, and ultimately left a 

 well-washed ground moraine of coarser material spread over much of the 

 county, but especially in the larger valleys, where the ice had been 

 thickest and the consequent floods greatest and most prolonged. These 

 Drift Gravels or Mid-glacial Gravels rest either upon the denuded surface 

 of one of the Mesozoic rocks, or unconformably upon the earlier sand or 

 gravel beds (as may be well seen at Hillmorton) ; they are usually well 



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