PORTLAND EOCKS OP EK(JLAND. 219 



No. 6. The glauconitic beds. These appear to have been seen in 

 several places by Dr. Fitton where I can now find no exposure. At 

 the Lodge-Hill cutting such stone is just visible, but there is not 

 more than 16 feet between the top and the Kimmeridge Clay. In 

 the brickyard at Hartwell, about 6 feet of very glauconitic material 

 almost immediately overlies the Kimmeridge Clay. Similar rock is 

 continued northwards to the Warren, Stukeley ; and to the south of 

 the area in the section at Brill, 5 feet of glauconitic matter is found 

 beneath the rubble bed No. 4. These contain hardened masses of 

 stone full of broken fossils, and at the base a pebble-bed full of 

 Lydian stones. I have recorded only Ammonites boloniensis, A. 

 pseudogigas, and A. hiplex from these beds ; but they have not been 

 properly searched. 



No. 7. The last of this series are argillaceous sands which lead 

 down into the Kimmeridge Clay, but are not distinctly glauconitic. 

 Like the lowest bed at Swindon, they chiefly differ from the true 

 Kimmeridge Clay in being barren of fossils ; and the two can scarcely 

 be separated at Hartwell, while at Brill only 6 feet are seen. On 

 the other hand, Dr. Fitton has recorded a thickness of 30 feet of 

 sands near Thame, and stated them to contain huge calcareous doggers 

 like those met with at Shotover. I have not been able to confirm 

 this ; but I think they must be a development of this part of the 

 series. 



The whole thickness of the Portland rocks in this district can thus 

 be estimated on the average to be no more than 60 or 70 feet, 

 in eluding the sands at the S.E, corner. Thus a great reduction has 

 taken place from Oxfordshire, and still more from Wiltshire. A 

 similar reduction is seen in the underlying Kimmeridge Clay, as 

 Exogyra virgida is reported a short distance below the pits at Hart- 

 well. This reduction, however, is mainly due to the thinness of the 

 Portland Sands, while the expansion or contraction of the Stone de- 

 pends upon how it is related to the more southern deposits, which 

 we must now proceed to discuss. 



In the first place it is obvious that we can trace the same sequence 

 in Oxfordshire as has been described in Bucks. The brashy beds 

 above, the more consolidated beds below, with their base full of 

 Trigonice, with Ostrea expansa and Pleuromya teUina, underlain by 

 non-glauconitic sand, are all repeated ; and in the space below are 

 glauconitic beds and non-glauconitic concretionary sands. While, then, 

 the tendency in the two counties is obviously for the sands to somewhat 

 change their character by the dying-out of the concretionary bods as 

 we pass to the north, the upper part remains sufficiently constant to 

 justify us in seeking still further relations with the beds in Wiltshire, 

 Bourton being no further removed from Great Hazeley than the latter 

 is from Stukeley. 



There are but two interpretations of the Buckinghamshire and 

 Oxfordshire beds which can be advanced with any show of reason. 

 The first and perhaps most natural assumption without particular 

 study is, that we have here thin representatives of all the Portland 

 deposits elsewhere reaching a far greater thickness. The other is, 



q2 



