A HISTORY OF NORTHAMPTONSHIRE 



TYPICAL SECTION OF THE GREAT OOLITE SERIES 



Description of the Beds 



Approximate 

 maximum 

 thickness 



I. 



2. 



CoRNBRASH : White, ruddy, or blue limestone, very fossiliferous, with 



/Ammonites macrocephalus, A. discus, etc. 

 Forest Marble Series : Variegated clays, hard flaggy blue-hearted 



limestones, shales, and oyster-beds, etc. 

 Great Oolite Clay : Blue and purple clay, with wood and car- 

 bonaceous matter, and ironstone 

 Great Oolite Limestone Series : Hard shelly limestones in courses, 



with marly or oyster-bed partings. Ammonites gracilis 

 Upper Estuarine Series : Very variable 



{a) Green, grey, or blue clay, or marl, with vertical plant-markings 

 and carbonaceous matter 

 * {b) Hard blue-hearted limestone, marl, hard shale, or oyster-bed (6 ft.) 

 (f) Blue, dark brown, or nearly white clay, with vertical plant- 

 markings, or carbonaceous matter ; or possibly an oyster- 

 bed. Ironstone at base 



ft. in. 



15 O 



8 o 



12 O 



25 O 



30 



90 o 



* Water-bearing. 



The Upper Estuarine Series 



The scale of the accompanying map does not permit of the 

 divisions of the Inferior and Great Oolite series being separately and 

 respectively represented on it, hence the connection between the two sets 

 of Estuarine beds is not seen. Speaking generally, in the valley of the 

 Nene the two Estuarine series come together, and in the valley of the 

 Welland they are separated by the Lincolnshire Oolite. 



The Upper Estuarine beds are even more variable than the lower in 

 thickness and character over large areas. They also undergo rapid 

 changes in the same area. In some places from eight to ten very 

 distinct beds might be chronicled, but a three-fold division (see Typical 

 Section) answers for most purposes. 



The occurrence of carbonaceous matter, large pieces of wood in 

 some places vertical plant markings in others, and limestones, as well as 

 both marine and fresh or brackish water mollusca — Modiola, Ostrea, 

 Cyrena and JJnio, etc. — point to such variable conditions as could be best 

 secured in the estuary of a large river, hence the name given to them by 

 Prof Judd. Probably the finest section ever exposed within the county 

 was at Roade Cutting, on the L. & N.-W. Railway, but a very good one 

 could recently be seen in one of the ironstone workings near to Finedon. 

 In the eastern parts of the county a nodular fossiliferous ironstone, about 

 one foot thick, occurs at the base ; and even in the western, midland and 

 other parts, where the two Estuarines come together, in almost all cases a 

 ferruginous band marks the junction. The commonly irregular junction, 

 with its ferruginous band, is supposed to indicate an unconformity 



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