GEOLOGY 



IN the following pages it is proposed to give, as far as possible, a 

 geological history of Northamptonshire as a succession of physical 

 events in defined time periods, and to use the composition and 

 natural sequence of the rocks, as well as the present configuration 

 of the ground, or modern scenery, chiefly in evidence. 



Geological Maps 



On looking at the geological map which accompanies this descrip- 

 tive matter, it will be observed that the county is coloured in what may 

 appear to be a very erratic manner. Each colour is supposed to represent 

 the area over which a particular rock formation outcrops, or is otherwise 

 exposed at the surface. The colours are of course purely conventional. 



The expression ' supposed to represent ' is used advisedly, for over 

 a considerable part of the county is spread a mass of gravel, sand, or clay 

 of glacial origin, which partially or wholly obscures the particular 

 formation represented on the map. The term ' Glacial Drift ' or simply 

 ' Drift ' will be used in a comprehensive sense to include the deposits of 

 all kinds and of relatively different ages directly or indirectly due to ice 

 action. In the maps of the Geological Survey, on the scale of one inch to 

 the mile, the chief areas covered with this confusing Drift are provisionally 

 indicated by lettering, and where the covering is so thick as to leave the 

 extent of the immediately underlying rock in doubt, dotted boundary 

 lines are used for the latter. In some cases there is uncertainty as to 

 whether the rock represented is even present. 



It may be noticed on the map that the colours tend to form 

 bands lying approximately from north-east to south-west ; this direc- 

 tion of outcrop is spoken of as the ' strike ' of the beds, and along it 

 they preserve more uniformity of height above ordnance datum than in 

 any other direction. 



The general ' dip ' of the beds is towards the south-east or at right 

 angles to the strike, so that in traversing the county from north-west to 

 south-east newer rocks successively occupy the surface without any 

 concomitant rise of the ground level, but rather the reverse. In the 

 direction of the county's greatest length however, which is nearly that 

 of the strike, a single formation, the Great Oolite for instance, may be 

 met with at the surface almost uninterruptedly from one extremity to 

 the other. 



We now proceed to give in tabular form the various geological 

 formations to be found in the county, together with their most distinctive 

 characters and approximate maximum thicknesses. Further details with 

 regard to each will appear in succeeding pages. 



1 



