GEOLOGY 



As the southern counties of England were not glaciated when 

 Northamptonshire was, so at an earlier period Northamptonshire was not 

 when more northern counties were. Certain accumulations of sand in 

 old depressions (valleys) of Pre-glacial age, sometimes described as Pre- 

 glacial deposits,' may have been formed contemporaneously with the 

 Pliocene beds of the east coast, but they may have been formed later, 

 and since they are certainly connected with glacial conditions not far 

 away, they will receive attention in the next section. 



The Glacial Period 



Clear evidence exists of two distinct periods of refrigeration in 

 Northamptonshire, and of three periods of diluvial action, corresponding 

 with the advent, temporary recession, and final decline of glacial con- 

 ditions. A common-sense view of what would be likely to happen 

 during the advance and retirement of an ice sheet appears to afford 

 an adequate explanation of the extra-ordinary phenomena of the Drift 

 deposits. 



Considering the main mass of a glacier to have passed from snow, 

 through neve, to compact ice, a great thickness of ice presupposes a 

 plentiful supply of moisture, but not necessarily great cold, indeed 

 a mean annual temperature not far below the freezing-point of water 

 would suffice for glacier formation. Northamptonshire was never far 

 from the southerly limit of complete glaciation, and so probably 

 fulfilled the above conditions. 



Suppose an ice sheet advancing from the north. This would 

 necessarily imply, either as a cause or effect, a lowering of the mean 

 annual temperature, but is quite compatible with warm, if short, 

 summers during which the melting of local snow and ice would give rise 

 to great floods, and these would distribute sand and gravel derived from 

 local rocks along their course of flow, the old river valleys, whilst disen- 

 gaged blocks of ground ice and masses of frozen ground would disturb 

 the soft wet clays on which they impinged or grounded. Most of the 

 evidences of this preliminary glacial (or pre-glacial) action were necessarily 

 obliterated by subsequent events, but some remain. 



There are certain sand beds, from 20 to 40 feet in thickness, 

 with a width varying up to half a mile, occupying an elongated depres- 

 sion, which have been traced for about eight miles on the south side oi 

 the Nene valley, through the parishes of Heyford, Bugbrook, Rothers- 

 thorpe, Milton, Collingtree, Courteenhall, and beyond towards Pid- 

 dington. These sands, finely laminated and apparently quite free from 

 erratics, are certainly to great extent derived from the Northampton 

 Sand. Recently these beds were cut right through at Courteenhall for 

 draining purposes, and it was then seen that at and towards the base 

 of the cutting gravel rather than sand predominated, that this gravel 



* John W. Judd, ' The Geology of Rutland,' etc., Memoln of the Geological Sur-vey, 

 p. 240. 



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