510 ME. M. ODLING ON THE [Oct. I913, 



The beds in the Great Oolite cannot be correlated in detail ; but 

 Mr. Eichardson considers that Bed 21 of Ardley (the Roach Bed) 

 may represent the Dagham Stone of the "White Limestone division 

 in the neighbourhood of Cirencester. 



North of Peterborough these beds do not appear to me to be 

 represented, the Cornbrash resting directly on the so-called 'Great- 

 Oolite' clays. Except in two places (see p. 502), the Bradford-Clay 

 facies does not seem to be developed ; while, but for their very 

 small thickness, the Forest Marble and Cornbrash are apparently 

 quite normal. 



In order to understand the conditions prevailing during the 

 deposition of the Bathonian rocks in the Oxford district, it is 

 necessary to consider what conditions prevailed during previous 

 times. At Fawler there is evidence that a barrier was being 

 formed a short distance away to the north ; the rising of this 

 barrier caused the Middle, and more especially the Upper, Lias to 

 be very thinly deposited, so much so that in a band only 3 inches 

 thick, among others, the following ammonites occur : — Harpoceras 

 cf. falciferum, Dactylioceras commune, and Hildoceras bifrons. 

 Above this band comes about 12 feet of unfossiliferous clay, 

 followed by the Upper Trigonia Grit and Clypeus Grit, which 

 form the ParJdnsoni Beds of^the Inferior Oolite, this zone over- 

 lapping all the lower zones. 



During the same time, north of this barrier, sands, for the most 

 part unfossiliferous, were being deposited, which have usually been 

 called the ' Northampton Sands,' although in reality they are not 

 equivalent to the true Northampton Sands, which are of earlier 

 date, but are in part homologous with the Clypeus Grits, as 

 Mr. Walford has shown. 1 



These North Oxfordshire Northampton Sands (to use the general 

 term, since no distinctive name has been assigned to them) are 

 well exposed near Westcott Barton and at the tunnel-mouth near 

 Fritwell in the Ardley section. South of this there is no definite 

 record of them; they certainly do not occur in the Oxford City- 

 Brewery "Well, and it is extremely doubtful whether they occur as 

 far south as Bicester, although the well-section at Gowell Farm 

 and Upper Arncot suggests their presence. 2 



We see, then, that a ridge lay north of Fawler and Stones- 

 field, curving round to the south of Fritwell, and possibly passing 

 under Bicester ; north of this ridge bands of sand were deposited, 

 while on the south the Clypeus Grits were deposited, the latter 

 probably thinning-out towards Stonesfield and not being laid down 

 as far east as Oxford. 3 



1 ' On the Eelatiou of the so-called " Northampton Sand " of North Oxon to 

 the Clypeus Grit ' Q. J. G-. S. vol. xxxix H8S3) p. 224. 



* E. H. Tiddeman, 'Water-Supply of Oxfordshire' Mem. Geol. Sarv. 1910, 

 pp. 26, 29, 67. 



3 The absence of Neseran Beds in the Calvert Boring suggests that the 

 boring lies on this ridge, which continued to assert itself certainly until late 

 Stonesfield-Slate times. 



