OP THE N.W., MIDL.Vl^D, AND EASTERN COUN'TIES. l79
in many places covers the middle sand-and-gravel formation, as
around Whittington, Oswestry, &c. South of Ellcsmere it capriciously
caps the large sand-and-gravel mounds (eskers ?), covers portions
of their sides, or lurks in the hollows between them ; but the sharp
line between the npper clay and the underlying gravel or sand, so
strikingly displayed all around the Irish Sea, is frequently absent.
The subglacial mud, or source of supply in the Lake-district (to
which the uniform character of the clay over extensive areas is
chiefly owing), would appear to have been carried by the currents
which floated the boulder- laden ice in a southerly direction by way
of Whitchurch and Shrewsbury to Berrington, where the Upper
Boulder-clay is scarcely distinguishable in appearance from the
horizontally continuous formation in Cheshire and Lancashire*.
In the extensive clay-pits lately opened near the Shrewsbury new
barracks the clay is a facsimile of the Upper Boulder-clay of
Cheshire and Lancashire, and the same in composition with the
exception of the absence of lime, which apparently did not fi.nd its
way from the Carboniferous rocks of the southern border of the Lake-
district so far south as Shrewsbury. In these claj'-pits there is
generally a sharp line between the clay and the underlying sand,
which in some places is contorted, and which is said to reach a
thickness of 90 feetf. Most of the erratics in the clay are from the
Welsh borders. Not more than one out of several hundred consists
of granite J. The stones are generally angular or sub angular ; and
exceedingly few of them are flattened or distinctly striated. jN'ear
the ferry, a short distance south of the Shrewsbury Welsh bridge,
the upper clay, somewhat in the form of a wrapper, covers a large
mound of shelly sand and fine gravel, in the lower part of which several
granite (Eskdale and Criffel) boulders have been found (see fig. 1).
The upper clay, more or less underlain by sand, is well represented
Fig. 1. — Section near tJie Shrewsbury Welsh Bridge.
A, Upper Clay. B. Sand and fine grayel. C. Talus.

• I had not discovered this southerly extension of the upper clay when my
  

paper on sections around the estuary of the Dee (Quart. Juurn. Geol. Soc. for
Kovember 1877) "was -written.
t The sand contains streaks and fragments of coal.
\ Granite, however, is rather abundant in the lower unstratified gravel of