412 
THE CRETACEOUS ROCKS OF BRITAIN. 
shown; combining the notes taken by Mr. Strahan and Mr. Hill, 
the section is as follows, the limits of the three zones being indi 
cated by the brackets : — 
ft. in. 
Zone of f Modular chalk with grey flints - - - ? 10 0 
//. planus, ( Nodular chalk without flints - - 5 o 
'Thin seam of grey marl. 
Smooth white chalk ----- 7 6 
Dark marly clay ----- 0 1 
Hard chalk ------- 6 0 
Terebra - Layer of green-coated nodules- - - - 0 3 
tulina / Nodular chalk ------ 2 4 
Zone. Smooth chalk -------40 
Fault Plane. 
Smooth chalk in thick beds, with partings of 
marl at intervals of 2 to 4 feet; Ter. gracilis 
V var. lata , about - - - - - 75 0 
Zone of f Hard white chalk in thicker beds, with 
R. Cuvieri. f Rh. Cuvieri and moc. mytiloides-seen for - 15 0 
About 125 0 
Mr. Strahan remarks that “ the fault mentioned above runs 
W. 15° S., very nearly along the strike of the strata which it throws 
down to the north, its effect being to depress out of sight an un¬ 
known thickness of the upper beds of the Middle Chalk. The 
dip points a little way west of north at 42°.” 
The lov T er part of the Rh. Cuvieri zone with the Melbourn Rock, 
about 40 feet in all, resting on the Belemnite marl, is exposed in an 
old pit now r occupied by farm buildings about half a mile east of 
the above. This is the pit mentioned by Professor Barrois in 1875, 
from which he obtained Inoceramus mytil aides, Rhynchanella 
Cuvieri, and Cidaris hiruda. 
Southwards by the Garstons and Gatcombe Down there are no 
good sections, but the base of the Middle Chalk caps the bold escarp¬ 
ment of Chillerton Down, and Mr. Strahan states that the Mel 
bourn Rock is exposed at the top of the large quarry at Shorwell, 
but in 1887 it was inaccessible. Professor Barrois records fossils 
from Shorwell ([no. labiates zone) in his list, so that he must have 
found some accessible exposure there. * 
No other good sections present themselves till v r e reach the west 
end of Brixton Down, where the upper part of the zone, with much of 
the overlying nodular chalk, is well exposed in the highest quarry on 
the north side of the Calbourne and Brixton road. The section here 
was first described by Mr. Whitaker in 1865,* next by Professor 
Barrois in 1875,f and lastly by Mr. Strahan in the Survey Memoir 
(1889.) The line of black clay which usually occurs from 6 to 8 feet 
above the green-coated nodules was seen by both the earlier observers, 
but was not visible in 1887, owing probably to some local squeezing 
or faulting in the face then exposed. In 1897, however, Mr. Hill 
* Quart. Journ. Geol. Soc., Vol. xxi. p. 402. 
t Description Geol. de la Craie de Pile de Wight, p. 18. 
