110 
THE CRETACEOUS ROCKS OF BRITAIN. 
the Chloritic Marl, but abound in the Chalk Marl 20 or 30 feet above 
it, such as Am. [Acanthi] rotomagensis, Scaphites cequalis, Baculitcs 
bcicuioides, and Turrilites costatus. 
The Chalk above the basal glauconitic stratum is firm, blocky, and 
greyish-white, but dries nearly white. It is not a chalk marl in a 
lithological sense, but a nearly pure chalk, that is to say, it contains 
hardly any argillaceous matter, and only a little fine sand or silt. 
Fossils are rare, and only a few of the commonest bivalves have 
been found, so that we are unable to say how much of it is referable 
to the zone of Am. varians. The lower part often contains flints of 
a peculiar kind ; these consist of a thick outer mass of whitish 
silica or siliceous chalk, with an internal nucleus of black flint; the 
centre shades into the white envelope and the latter into the sur¬ 
rounding chalk, so that till broken they look like hard lumps of 
chalk. These flints only occur in the lower 20 or 30 feet. The 
higher beds are without them, and consist of still whiter and more 
compact blocky or bedded chalk, which resembles the higher part 
of the Lower Chalk elsewhere. 
Near the top of the Lower Chalk there is generally some thick¬ 
ness of greyish or yellowish marl, usually from 6 to 10 feet of such 
material; this is the Belemnite Marl or subzone of Actinocamax 
plcnus, though that fossil has only been found at one or two places. 
A.—The Basement Bed. 
In the more eastern part of the district under description, that 
is, around Melcombe Bingham and Melcombe Horsey, the top¬ 
most bed of the Selbornian is a glauconitic sandstone so lull 
of dark brown phosphatic fragments and fossils that it may 
be termed a phosphatic conglomerate. Upon this rests the 
nodule-bed which forms the base of the Lower Chalk (zone 
of Am. varians). Where this facies prevails and where exposures 
are weathered it requires care to collect separately from the two 
nodule-beds, but where sections are clear there is no difficulty. 
The existence of a well developed nodule-bed above the 
phosphatic conglomerate at these localities was not known to 
me in 1899, and was not -recognised by Mr. Rhodes when 
he collected there in 1894 ; consequently 1 have no doubt that, 
of the fossils then obtained by him and recorded as from the 
topmost bed of the Selbornian in the first volume of this 
Monograph (p. 108 et. seqi), some few really came from the basal 
bed of the chalk, and are wrongly included in list there given. 
Such probably are Am. [ScJtloenbachia] varians, Am. [$c/A] 
Coupei, Turrilites costatus and Cucullcea mailleana. 
Mr. J. Scanes, who visited this district in 1901 and found 
a good exposure of the/ junction-beds at Dorsetshire Gap, north¬ 
west of Melcombe Horsey, has kindly put the following notes at 
my disposal:— 
