476 PROCEEDINGS OP THE GEOLOGICAL SOCIETT. [June 3, 



to the south-east. (The Gault dips very gently to the north or 

 north-east.) I was not fortunate enough to make out this bed with 

 its fossils, and could see nothing that might not be shpped Gault. 

 There seemed to me no beds exposed below the green sandstone. 

 Ostrea Leymerii, however, is a very characteristic shell of the Ather- 

 field beds in England, and is not known to occur in the Gault or 

 in the higher members of the Lower Greensand. 



5. Wealden. — The beds which I take to represent our English 

 Wealden underlie undoubted Cretaceous rocks around most of the 

 border of the district, and cap the hills in the interior. They are 

 not seen on the coast at Wissant ; and coming inland there is at first 

 some difficulty in tracing the beds, in consequence of the blown sand. 

 I^ear Marquise, and on the north side of the road to Wissant, is a 

 sand-pit showing 10 feet of alternations of yellow, white, and buff 

 sand, well bedded, with lines of darker ferruginous sands and carbo- 

 naceous beds. There are in this section a great many small faults 

 (from 1 to 6 inches) ; and the pit seems to have been sunk in a small 

 synclinal, as the beds dip down on each side. 



East of the Calais road are some very interesting sections of 

 Wealden beds resting on Carboniferous Limestone. At Bois Sergent 

 they have been briefly noticed by Mr. Godwin-Austen*,who describes 

 them as " thick accumulations of gravel, sand, brick- earth, and 

 pipe-clay, with much vegetable matter, which have to be worked 

 through for the iron-ore beneath." I have little doubt that these 

 masses are mostly "piped" into the limestone, as is evident in a quarry 

 a little way south-west of the houses (Bois Sergent). Here sand, 

 clayey sand, and ferruginous sandstone are seen, clearly let down by 

 the dissolving away of the Limestone. A large pit, just north of the 

 houses, shows a considerable thickness of the same beds, with large 

 masses of limestone standing up below. Just west of the cross- 

 roads (west of Bois Sergent) a large pit showed a clearly cat section 

 of Wealden on one side and on the other large masses of limestone. 

 The Wealden beds were very irregular in position, and not constant 

 in character, giving in all probability a thickness of about 50 feet in 

 these pits. The lowest part showed : — 



YeUow and white sand, from 10 to 15 feet. 

 Mottled clay, 10 feet. 

 Ironstone, 5 feet. 



Above the sand came more mottled clay ; but I could not trace any 

 definite order here. 



]S"orth of Bois Sergent there are a great number of shafts about 

 50 or 60 feet deep, by means of which the ironstone is raised. One 

 of them showed in its upper part about 10 feet of brightly coloured 

 clay (yellow, red, purple, and variously mottled) ; from another T 

 got masses of blackish clay, with vegetable matter ; but, as I just 

 observed, it seems impossible to determine any definite order of 

 succession for these clays and sands ; most of the ironstone, however, 

 came from the bottom. 



■'' Quart. Joia*u. Geol. Soc. vol ix. 185o, p. 232, 



