THE GEOLOGY OF SOUTH ESSEX. 217
by Mr. Bristow, that "there is a spring at Hockley, the water of
which, like much of that in the London Clay, contains sulphate of
magnesia (Epsom Salt)." He adds that an attempt was made some
years ago to establish a Spa there, but the speculation proved a
failure, all that now remains being the buildings still known as
Hockley Spa.
The Lower Bagshot Beds, which are next in succession to the
London Clay, form the subject of chapter 17. This chapter is, as
regards Essex, mainly the work of Mr. H. B. Woodward, who was
one of our Guides during the Brentwood excursion last spring. These
Bagshot beds consist of certain outlying patches in the neighbour-
hoods of Brentwood, Ingatestone and Rayleigh. There is also a
capping of Bagshot Beds on Langdon Hill, as we learned during
our excursion there last year. It is pleasant to learn from Mr.
Whitaker that, with the exception of a piece of the cast of a
Turritella, found at Hampstead, the only recorded instances of
fossils from the Lower Bagshot Sands of the London Basin are
some casts of Turritella, Natica and Voluta, found at Mill Green,
north of Frierning, in Essex. They were discovered by those inde-
fatigable workers at the Bagshot Beds, Messrs. H. W. Monckton
and R. S. Herries, who were present among our geological Guides
at our Langdon Hill and Brentwood excursions.
In chapter 18, Deposits of Doubtful Age are discussed. These
are the Clay-with-flints, resulting from the slow decomposition of
the uppermost beds of Chalk from atmospheric action, and the Brick-
earth associated with it, together with certain patches of high-level
gravel. Chapter 19 deals with Glacial Drift. These beds, which
form almost the whole of the surface of the northern half of Essex,
appear chiefly in isolated patches south of a straight line drawn be-
tween Epping and Maldon. Mr. Whitaker discusses the reason
why the Boulder Clay outliers all stop short of the northern edge
of the Thames Valley, below London, together with the sand and
gravel of Glacial age. He thinks that the absence of Boulder Clay
south of the Thames points to the conclusion that the deposit never
extended much farther south than it now does, and that it must have
ended off against rising ground which existed in the present river
valley. And he quotes the view of Mr. J. Trimmer that the Glacial
Drift appears to have been cut off by a ridge of Eocene Tertiaries,
of which the Highgate Range and Shooter's Hill are probably the
remains. Certainly the Thames, as the extensive gravel and allu-
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