384 
LOWER OOLITIC ROOKS OP ENGLAND 
Pecten lens. 
Pern a rugosa. 
var. quadrata. 
Pholadomya dcltoidea. 
Heraulti. 
lyrata. 
socialis. 
Pinna ampla. 
Pteroperna costatula. 
plana. 
Quenstodfcia lanvigata. 
Tancredia axiniformi. 
Thracia curtansata. 
Trigonia costata. 
Moretoni. 
Unicardium varicosum. 
Bhynchonella concinna. 
varians. 
Terebratnla maxillata. 
Acrosalenia hemicidaroides. 
Clypeus Miilleri. 
Echinobrissus Griesbachi. 
Woodwardi. 
1 sastraoa. 
Thamuastra3a. 
GREAT OOLITE CLAY (BLISWORTH CLAY). 
These beds, so named by Prof. Judd,* present many cliaracters 
similar to those of the Upper Estuarine Series. They comprise 
variegated, blue, green, yellow, purplish, and black clays, with 
irregular sandy, ferruginous, and shelly bands. Layers of "beef " 
occur, also crystals of sclenite ; and lignite, nodules of ** race " and 
also of ironstone are met with. Very often there is a layer of 
ironstone-nodules at the base, but ferruginous bands occur also 
higher up. The beds are from 5 to about 40 feet thick but 
usually a thickness of about 20 feet may be expected. 
The term Blisworth Clay was introduced for the strata in 
1870, by Samuel Sharp: at the same time he employed the name 
Great Oolite Clay for the beds known as the Upper Estuarine 
Series. t Later on he used the term Great Oolite Clay instead 
of Blisworth Clay. If, hoAvever, a distinctive local term be used, 
that of Blisworth Clay should be adopted. 
Fossils, as a rule, are rarely to be obtained, but all those 
recorded are marine forms. Nevertheless, as remarked by Prof. 
Judd, it is not improbable that the strata are, in part at least, of 
estuarine character. The coloured clays which charaterize the 
strata, are suggestive of fluvio-marine conditions. 
Oyster-beds with Ostrca subruyulosa occur ; and it is notice- 
able that Placunopsis socialis., which is locally abundant, is else- 
where common in the Stonesfield Series. The beds are inti- 
mately linked with the Great Oolite Limestone below, and the 
division between them is mainly a lithological one that is not 
likely to be taken on a constant horizon. 
The beds may be regarded as generally equivalent to the 
Forest Marble. They are, however, of little economic value, and 
sections are consequently scarce. 
Allusion has been made to the attenuation of the strata in 
parts of Oxfordshire; and Prof. Judd remarks that, further 
to the north and north-east, in South Northamptonshire, &c., " it 
was found impracticable by the Geological Survey to map them 
separately, and hence they are in those districts grouped with the 
Great Oolite. As we go northwards into North Northampton- 
* Greol. Rutland, pp. 9, 32, 186, 214. 
f Quart. Journ. Geol. Soc., vol. xxvi. pp. 359, 380 ; and vol. xxix. p. 228. 
