NOTES ON A RECENT BLUE BOOK. 15
rivers. Here and there in these valleys the London-clay
appears. It underlies the other beds mentioned, and is the
oldest formation seen at the surface in this part of Essex.
A glance at the map shows that, as a general rule, the larger
towns and villages of the district exist where there is a broader
expanse of gravel than usual, as at Witham, Braintree and
Bocking, and Kelvedon. This, of course, arises from the fact
that a supply of water is always obtainable from the gravels
overlying the London-clay, though not from the London-clay
itself. And the London-clay hereabouts has an average thick-
ness of considerably more than 100ft. Thus, from the
Geological Survey Memoir on Sheet 47, Essex,2 we learn that at
Felix Hall, Kelvedon, the London-clay was 130ft. thick, at
Saling 165ft., at Braintree 126ft., at Witham 1541/2ft. at the
Waterworks, and 210ft. at Powers Hall, and at Coggeshall 120ft.
at Mr. Gardner's brewery and 155ft. at Swinburn's Isinglass
factory.
Of the two Coggeshall wells mentioned, that at Gardner's
Brewery ends in sand underlying the London-clay. But this is
exceptional, all the other wells mentioned ending in the Chalk,
which may be considered the source of water supply for deep
wells in this part of Essex, when the water from the gravels
above the London-clay becomes unsafe. Chalk is reached at
various depths between 200 and 300ft.
As regards site, Coggeshall is exceptional, because it stands
in a part of the valley of the Blackwater in which there is an
unusual extent of London-clay at the surface, though the
greater part of the village is on gravel. It has thus a much
smaller area available for shallow wells than Braintree and
Bocking, Witham or Kelvedon.
Dr. Fletcher informs us that, as regards water supply,
"there are many private wells in Coggeshall, but the majority
of the inhabitants obtain water from St. Peter's Well." Of the
quality of the water he is unable to speak. It is, however,
manifestly derived from the gravel and sand underlying the
Boulder Clay. Besides the supply obtained directly from St.
Peter's Well many of the inhabitants receive a supply from it
by means of a tank-cart, into which water from this well is
pumped, and received at houses in buckets.
2 Written by W. Whitaker. W. H. Penning, W. H. Dalton, and F. J. Bennett.