162 
the; cretaceous rocks oe Britain. 
2. Zone of Holaster subglobosus. 
The higher part of the Lower Ghalk, or that which represents the 
zone of Holaster subglobosus, presents an unusual aspect in this part 
of Wiltshire. The beds of compact whitish chalk, of which it usually 
consists, are here divided by layers or courses of hard, greyish, 
gritty chalk, which weather out conspicuously on account of their 
hardness ; moreover, a strong lens reveals the fact that they con¬ 
tain dark green or black grains of glauconite, a mineral which is 
seldom seen elsewhere at so high an horizon. There are sometimes 
three or four such courses of hard chalk, varying in thickness from 
1 Jj to 3 feet. At the top of this chalk the Belemnite marl or sub¬ 
zone of Actinocamax plenus is probably always present, though it 
is not often exposed. 
The exposure of these higher beds in the lane above Eastcott has 
been described on p. 158. Some of them can also be seen in the lane 
south of Urchfont. 
The chalk in the cutting on the railway a little north of 
Collingbourn Kingston, may be in this zone (see p. 158). 
On the north side of the Vale the higher beds are well shown 
in the roadway north of Allington. A succession of hard beds, 
live or six of them, cross the road, and form a set of steps or ridges. 
One about 80 feet below the Melbourn Rock is a hard grey siliceous 
chalk, containing much globular silica, and this may be taken as 
the top of the Am. varians zone. About 40 feet higher is a very 
gritty limestone, compact and heavy, with small grains of dark 
green glauconite ; its grittiness being caused by minute fragments 
of Inoceramus shell, many of which are silicified. * 
List of Fossils from the Chloritic Marl and Lower Chalk 
of North Wilts. 
The following lists of fossils have been drawn up from several 
sources. As regards the Chloritic Marl, the entries under the heads 
of Urchfont, Stert, and Calstone are those of fossils obtained and 
identified by myself; those from Devizes were obtained by Mr. W. 
Cunnington, and are now in the Museum of the Geological Survey ; 
those from Chiseldon are in the Museum of the Marlborough College 
Nat. Hist. Society. 
Of the Chalk Marl lists, that from Savernake includes those 
mentioned by Mr. Codrington; those from Clyffe Pypard, 
Bincknoll, and Chiseldon are from collections made by the mem¬ 
bers of the Marlborough Coll. Nat. Hist. Soc., published in the 
Reports for 1889, 1897 and 1901; most of these fossils were sent 
to me for identification. 
* 
See Quart. Journ. Geol. Soc., VoL xlv. p. 411 . 
