UPPER ESTUARINE SERIES. 315 



MIDLAND COUNTIES. 



Great Oolite Series. 



This Series is divided as follows : — 



Cornbrash (seep. 307). 



Great Oolite Clay. 



Great Oolite Limestone. 



Upper Estuarine Series, and Northampton Sand (upper part, local). 



Tipper Estuarine Series. 



This division, named by Prof. Judd in 1867, consists of light-blue, 

 grey, and variegated clays, sometimes very sandy, together with lami- 

 nated marls, shales, and irregular beds of limestone, and "beef" 

 (fibrous carbonate of lime). The beds are from fifteen to thirty feet 

 in thickness, and contain wood and other plant-remains, and also 

 shelly bands with marine and freshwater mollusca. At the base is 

 a thin band of nodular ironstone, rich in fossils, which marks the 

 junction betw-een the Great and Inferior Oolite Series ; and, in 

 Prof. Judd's opinion, affords evidence of a break, accompanied by 

 slight unconformity, between these two Series in the Midland area. 



Mr. Sharp observes that the Upper and Lower Estuarine series 

 occur together in vertical juxtaposition throughout a large part of 

 Northamptonshire and in Oxfordshire. In Oxfordshire he observes 

 that the Upper Estuarine Series is traceable to the Stonesfield 

 Slate, and the difficulty of separating the two Estuarine Series led 

 formerly to the whole of the Northampton Sand (Lower Estuarine, 

 etc.), being regarded as the equivalent of the Stonesfield Slate. 

 Among the fossils are species of Pholadomya, Modiola, Ostrea, 

 Cyrena, Unio, etc. ; remains of Ceteosanrus also occur in the beds. 



All the characters presented by the Upper Estuarine Series, 

 according to Prof. Judd, point to the conclusion that the beds were 

 accumulated under an alternation of marine and freshwater con- 

 ditions, such as occurs in the estuaries of rivers.^ 



The beds may' be seen at Ketton and Casterton, near Stamford, 

 and in the Essendine and Danes Hill cutting of the Great Northern 

 Railway ; ' also near Duston and Dallington, west of Northampton. 



The Clays in this series are worked for brick-making, at Stamford, Little 

 Bytham, and other places ; at Wakerley a fire-clay occurs which has been used in 

 the manufacture of terra-cotta. The soil is comparatively barren, being stiff and 

 cold. 



Great Oolite Limestone. 



The Great Oolite Limestone, so named by Prof. Judd, consists 

 of alternate beds of compact white marly limestone and clay, with 



^ Geol. Rutland, etc., p. 32 ; Jukes-Browne, Geol. S.W. Lincolnshire, p. 61. 

 - J. Morris, G. Mag. 1869, p. 103. 



