CORRELATION OF THE BOURNEMOUTH BEDS. 215 
and compact bed, 12 feet thick, of glauconitic sandy clay, with green 
grains and with occasional lignitic layers, very similar in appearance to 
some of the Highcliff beds described by Mr. Fisher*. This bed rises 
at the 8.E. corner of the promontory, and at its N.W. end is at least 
30 feet above the beach. It includes scattered, round, black flint 
pebbles throughout, and has a continuous layer of them at its base. 
This and the succeeding beds rise at an angle of 2° or 3°. Like the 
preceding, it does not extend along the coast beyond the Head itself. 
At Alum Bay the position of the two beds last described is occupied 
by similar sandy clays, 71 feet thick, becoming more sandy towards 
the base and containing five layers of lignite, and capped by a thin 
seam of red sandy clay, answering probably to the orange-coloured 
bed at the base of the Highcliff sands. 
Boscombe Sands.—The next series is perfectly distinct and may be 
called the Boscombe Sands. It represents the principal mass, 148 feet 
thick, of brilliant-coloured sands at Alum Bay (numbered 25 to 26 
in Prestwich’s section, see fig. 6), containing thin straggling layers of 
flint pebbles with small rounded fragments of quartz. These beds, at 
Hengistbury Head, are only seen in the longest or 8.W. range of 
cliffs, towards the centre of which they gradually rise from the 
beach. From the point at which they rise until a thickness of 7 
feet or 8 feet is exposed, they are whitish or ash-coloured sand, con- 
taining much scattered lignitic matter, with layers of pebbles about 
3 feet apart. The layers are, however, not persistent, and we find 
within a few yards a 3-feet bed of sand between two pebble-layers 
thickened to 12 feet, and including four layers of pebbles; nor are 
the pebbles always confined to layers. Under the white are pinkish, 
black, and deep chocolate-coloured sands 17 feet thick, again under- 
lain by 7 feet of white sand. The junction between the dark 
coffee-coloured sands (which become black after a few minutes’ ex- 
posure to the air) and the upper white sands is remarkable, the 
white sands haying cut through and imbedded angular pieces of the 
darker sand of all sizes up to 4 or 5 feet diameter. The surface of 
the dark sand as well as some of the larger detached pieces have been 
bored by Teredo or Pholas before being imbedded (fig. 4, p. 216). The 
dark sand has basin-shaped patches of pinkish ash-coloured sand at 
the top, the pink sand sometimes forming a layer 1 foot 6 inches thick 
above the pebbles, so that the latter do not always mark the junc- 
tion. Nearer the neck of the headland the bottom white beds become 
thicker and more compact, and contain iron layers and small con- 
eretions. he dark beds are very variable and change colour within 
short distances. 
For half a mile the cliffs are very low, being but 17 feet high near 
Double Dykes, and composed of shingle, showing here and there at 
their base the uneven and eroded surface of the Boscombe Sands, 
which are now yellowish white. Here these loose sands and 
pebble-beds have been a prey to subsequent denudation, which, 
however, had not force to remove the included heavy shingle, 
but has left it in solid masses 12 and 15 feet thick, mixed with the 
* ©. Fisher, Quart. Journ. Geol. Soc. vol. xviii. p. 86. 
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