Inverted Mass of UpiJer Cretaceous Strata. 13 



above the Lower Greensand in pits near Leighton Buzzard, and also 

 in pits adjacent to Harris's at Shenley Hill, as well as in others 

 further away to the east and west of the hill. The study of these 

 sections enabled us, at the same time, to identify the beds between 

 the " silver-sand " and the brachiopod-limestone at Harris's Pit. 

 Finally, information was sought as to the succession of beds between 

 the Gault and the Chalk Marl along the base of the Chalk escarpment, 

 some miles to the east and south-east. 



A. Characters and Correlation of the Gault in 

 Mr. Gregory Harris's Pit. 



It is a matter of surprise to us that this clay has ever been mis- 

 taken for Lower Gault. Its lowest part shows a pronounced marly 

 character, and differs from the true Lower Gault of the district 

 by the absence of sand and the rarity of glaiiconite ; it yields none 

 of the ammonites of the Lower Gault, but contains species 

 characteristic of the rostratus zone. 



To confine attention first of all to the lowest 8 feet. The well- 

 bedded rock above the lowest few inches has a blocky or sub- 

 conchoidal fracture ; it is of a very dark-greenish grey hue when wet, 

 but dries to a much paler colour. Though strongly argillaceous, 

 it contains a considerable proportion of carbonate of lime and it 

 shows minute glistening specks, which at first suggest that it is 

 somewhat micaceous. This appearance is due to tiny flakes of 

 carbonate of lime, probably derived from the thin friable shells of 

 a species of Anomia. 



With the exception of Beleninites minimus List., which is found 

 fairly abundantly a short distance above the base, fossils are not 

 easily obtainable in a state fit for identification. Inoceramus is 

 not uncommon, and there are apparently at least two species, one 

 of which is a flattened expanded form suggestive of /. crijJj^si 

 Mantell. Neither I. concentricus Park, nor /. sulcatus Park, has been 

 found in the lowest 8 feet, although prolonged searches have been 

 made. The presence of small impressions of the characteristically 

 ornamented Nautilus deslongchampsianus, d'Orb., indicates a 

 position in the rostratus zone or higher. This species has been 

 recorded from the Upper Greensand of Wiltshire {rostratus beds and 

 Pecten asper beds), but it is more distinctive of the Chalk Marl. 

 Ammonites occur in a band which, in different parts of the section, 

 varies in position from 2 feet to about 4 feet above the base of the 

 clay. They are poorly preserved, in a compressed condition, often 

 consisting of little more than brownish rusty films on the bedding- 

 surfaces ; nevertheless, many show plainly the main features. The 

 commonest form is closely comparable with well-known specimens 

 from the sandstones {rostratus zone) of the Upper Greensand of 

 Devizes and of the Undercliff, Isle of Wight, variously named in 

 museum collections as Hoplites auritus (J. Sow.), H. catillus (J. de C. 

 Sow.), or H. auritus var. catillus. 



