1873.] 



SHARP OOLITES OF NORTHAMPTONSHIRE. 



227 



this are three beds of the Great Oolite series, having a maximum 

 thickness of 45 feet — the lowest consisting of clay having a persistent 



Fig. 1. — Diagram of General Section, slioiving the 'position of the 

 Inferior Oolite Limestone and Divisions of Northampton Sand. 

 Blisworth Clay ( 2 ft.) . 



White Limestone. . . (25 ft.) 



Blue Clay (15 ft.) 



Ferruginous band 

 Place of Great Limestone of the Inferior Oolite 



'Upper ...( WhiteSand (12 ft.).... 



I Plant-bed 



> Great Oolite. 



f Line of un- 

 *\ t_ conformity. 



c 



Middle.. J Variable beds (30 ft.) 



Limestone. 

 /Slate 



....1 



Lower 



Beds containing "1 ,^ ^ .. 

 ■{ Ironstone ... J ^ '' 



}■ (4 ft.) { 



Amm- bifrons bed ... 

 Pebbly bed 



Upper Lias. 



ferruginous band at its base (which clay, containing wood, plants, 

 and numerous bands with fresh-water shells, and exhibiting other 

 estuarine characteristics, has been termed by Mr. Judd the " Upper 

 Estuarine Series ") ; the middle, of a series of marly limestones ; 

 and the uppermost, of clay characterized by an abundance of Ostrea 

 subrugulosa. 



The Middle Division of the Northampton Sand was separated by 

 me from the Lower Division (provisionally, as I stated) because of 

 the intervention of a band of coarse Oolitic Limestone, and because 

 of differences, throughout the district then treated of, in their 

 mineral and stratigraphical characteristics. 



To the north-east of Northampton, however, those differences are 

 not so marked : for instance, over a considerable area, in the Lower 

 Division, for ironstone is substituted an only slightly ferruginous 

 limestone ; and again, in other places, the Middle Division is 

 quarried for ironstone, being more richly ferruginous than the 

 Lower Division, while the Limestone band is frequently absent. 



In contrast to the varying, and therefore uncertain, marks of 

 distinction between the Lower and Middle Divisions of the North- 



q2 



