A HISTORY OF BUCKINGHAMSHIRE 



we find in Buckinghamshire a marine and estuarine group divided as 



follows : 



LOWER ESTUARINE SERIES 



NORTHAMPTON SANDS 



In parts of Northamptonshire and in Lincolnshire this group is 

 overlain by an important division known as the Lincolnshire Limestone, 

 which furnishes many a valuable freestone. No portion of it is repre- 

 sented in Buckinghamshire, and consequently there is a considerable 

 break between the representatives of the Inferior Oolite and Great Oolite 

 Series in the county. Locally also there are evidences of erosion between 

 the Upper Lias Clay and the succeeding Northampton Sands. 



Just beyond the borders of the county, in a brickyard north-east ot 

 Brackley, resting on the blue pyritic clays of the Upper Lias, there were 

 to be seen green and dark grey sands and hard ferruginous sandstone, 

 together 3 feet 6 inches thick. The stone contained Avtcu/a braam- 

 buriensis and some other fossils, and also pebbles of hardened Upper Lias 

 shale. These sandy beds, representing the Northampton Sands, were 

 overlaid by 8 feet of purplish loam, clay and white and brown sand, 

 perhaps belonging to the Lower Estuarine Series. 



In this neighbourhood however the lower beds of the Great Oolite 

 comprise an Upper Estuarine Series, and where the two Estuarine series 

 come together it is most difficult to distinguish between them, for in 

 characters they are alike, and it is only where one group is seen to rest 

 with marked unconformity on the other that any division can be made. 

 Further north in Northamptonshire the two are separated by the Lm- 

 colnshire Limestone, but the Upper Estuarine Series may be regarded as 

 the more persistent as it stretches unconformably across the eroded 

 faces of the subdivisions in the Inferior Oolite Series. 



The Northampton Sands are exposed in Buckinghamshire only along 

 the Ouse valley at Whitfield Mill below Biddlesden. Hard bands such 

 as occur near Brackley have been met with in borings on the north-east 

 of Stowe Park near Akeley and along the borders of the Ouse valley near 

 Stony Stratford ; but the evidence of their age is indecisive. 



There is no doubt that both Northampton Sands and Lower 

 Estuarine Series die out in a south-easterly direction from Northampton- 

 shire towards Olney and Stony Stratford. Together they appear to 

 represent in places the higher portion of the zone of Ammonites jurensts, 

 but they consist mainly of the zones of A. opalinus and A. M"*"""' r 

 in other words they are equivalent to the higher part of the Midford 

 Sands and the lower part of the Inferior Oolite of the west and south- 

 west of England. 1 



GREAT OOLITE SERIES 



This series, which occupies a considerable area in the northern part 

 of the county, is locally divided as follows : 



i 'Lower Oolitic Rocks of England,' Geol. Survey, pp. 33. 3 8 > etc - 



