I58 SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND.
probability have been pierced also at Chatham, had the boring been
deeper. Now in Dorsetshire, where the Oolitic beds above the Oxford
Clay are all well shown, their average combined thickness would
appear to be, according to Mr. H. B. Woodward, about 1,250 feet,
more or less. In the Boulonais, on the other hand, their thickness
is given by Dr. Barrois as about 765 feet, while at Battle, as we
have seen, it was 1,840 feet. The distance in a straight line from
the Isle of Portland to Battle is about 130 miles, and from Battle to
the Bas Boulonais rather more than 50 miles. It is noteworthy,
therefore, that while we meet with many hundreds of feet of Upper
Oolite beds both in the east and in the west, they wholly disappear
only 32 miles north of the intermediate place, Battle, at which they
are unusually thick. The presence of the Oxford Clay at both
Battle and Chatham makes this remarkable thinning away of the
Upper Oolitic beds towards the latter place, at the rate of 571/2 feet
per mile, a very striking example of what must very frequently occur
in the case of the shallow-water beds which make up the great mass
of our sedimentary rocks. And simply as enabling us to obtain an
admirable illustration of the rapidity with which such rocks thin away
in certain directions, the existence of the Sub-Wealden boring would
be amply justified.
Honey Buzzard (Pernis apivorus) at Little Baddow, Essex.—On May
l8th I shot a Honey Buzzard at Little Baddow. It proved to be a female in good
plumage; expanse of wings, 4 feet 41/2 inches ; weight, 28 ounces. On examining
the stomach I found it contained the remains of beetles, caterpillars, and egg-
shells. I was not previously aware they took eggs, but on picking the birds up I
noticed a quantity of yolk of eggs run from the crop from a hole made by the
shot. I have never seen this bird so early in summer ; it generally visits us in
September. There being few bees or wasps about might perhaps be the cause of
its taking eggs.—C. Smoothy, Little Baddow, in "Field," June 2nd, 1888.
Migratory Swarm of Libellula quadrimaculata off the Essex Coast.
Mr. John Cordeaux, of Great Cotes, Ulceby, writes thus to the "Entomologists'
Monthly Magazine" (vol. xxv., 93) under date July 26th, 1888 :—"The following
came this morning from the master of the 'Swim Middle' light vessel, off the
Essex coast:—' I do not know whether the insects will be of any interest to you,
but being strangers to me, I take the liberty of sending them. On June 23rd,
from 6 to 8 p.m., a flock of them came on board and rested on the ropes, and
even on the cable the vessel was moored with from the bows down close to the
water's edge. The wind was E. by S., and the weather fine and clear, and I
told the man on watch to catch a few, which I forward. I never saw anything
like it before.—S. Pender, 21, Abbott Road, Poplar, E., July 24th, 1888.'"
On this, Mr. R. McLachlan, F.R.S., remarks:—"The insects are Libellula
quadrimaculata, in both sexes. Enormous migratory swarms have many times
been remarked on the Continent. The species is no rarity here, but somewhat
local, and I think this is the first record of a migratory swarm in this country.
The 'Swim' is not far from Shoeburyness, and therefore practically at the
mouth of the Thames. According to the direction of the wind they, in all proba-
bility, came from Holland and contrived to arrive just before nightfall."