ON THE GRAYS AND UPMINSTER RAILWAY. 147
even now be seen on the Thames in very severe winters, and a very
slight reduction of our winter temperature would suffice to make
them of more frequent occurrence and of a greater average size.
It is the more necessary to point out that the glacial action—
if any—required to produce the effects considered is merely that of
ordinary river-ice, inasmuch as there is a general tendency at present
not only to consider many appearances as glacial which are by no
means necessarily glacial at all, but also to ascribe all evidence of
ice-action to the Glacial Period. I have, therefore, ventured to
remind the reader both that phenomena of this kind need not
necessarily be the work of ice, and that ice did not cease to be a
geological agency when the epoch known as the Glacial Period came
to an end.
Chalk, as I have already stated, may be seen towards the bottom
of the cutting as far as the Back Lane Bridge. North of the bridge,
however, Thanet Sand appears below the gravel, and is visible as
far as the cutting extends. East of Combe Wood the ground
gradually slopes downwards to the level of the alluvium of the
marsh bordering the Mardyke on both sides, and the cutting is
replaced by an embankment. In this sectionless space adjacent to
the stream the Woolwich and Reading Beds come on above the
Thanet Sand, the dip being northerly. On crossing the Mardyke
we found that a cutting south of the road from Aveley to Stifford
showed us London Clay capped by a little loam containing a few
pebbles.
North of the Aveley and Stifford road but little excavation had
been done at the time of our visit.1 However, having arrived at the
London Clay, we had the satisfaction of knowing that the sections
we had seen were those of the most geologically interesting part of
the line. For northward as far as Upminster, whatever may be the
attractions of the new railway in other respects, the only geological
formations likely to be exposed are London Clay with a capping of
gravel or loam, as shown on the map of the Geological Survey
(1, S.W.). As regards the portion we traversed, it becomes evident
that if the geological surveyor could have had our advantages, he
would have somewhat curtailed the western end of the Tertiary
outlier on which Belmont Castle stands ; while he would have
1 On July 16th, I found that the course of the railway N. of this road was nearly due north.
and, on the average, about 200 yards west of the road between Stifford and South Ockendon. It
was marked out for a distance of about three-quarters of a mile. Here and there were hole"
showing 3 to 4 ft. of gravel. Water at their bottom indicated the existence of London Clay a
short distance below.
L 2