THE DISTRICT AROUND CHELMSFORD. 173
several of which have from time to time been described in the pages
of the Essex Naturalist, and Mr. Rowe's interesting paper on the
subject is still fresh in our minds. His description of the boulders
found round Felstead and the neighbourhood equally applies to those
occurring in the Roothings, where, as he says, with regard to his
district, the Jurassic boulders seem to be the most abundant. I
have been able to identify many of them through the kindness of
Mr. B. B. Woodward, of the British Museum, to whom I am much
indebted in this respect.
Among others there are blocks of micaceous schist, dolerite, and
felsite, whilst blocks of quartzite and sandstone are very frequent.
I have brought with me to-night a very interesting boulder of garnet
gneiss rounded on one side, and polished and striated on the other,
which happens to be of a rather more convenient size to carry about
than some of the others. There is also another small nodule of Red
Chalk, which Mr. Woodward considers probably came from Lincoln-
shire, and which is the only specimen I have heard of belonging to
this formation. It was dug out from the white Boulder Clay five feet
from the surface, in a pit at the "Sycamore," Roxwell.
I have referred above to the uniform appearance of the Boulder
Clay, but the term "uniform" is hardly applicable to the case, as,
contrary to the generally received idea, there are two distinct strata
of the Roothing Clay, the top stratum being of a yellowish colour,
and the bottom dark blue or slaty, when first exposed, but weather-
ing afterwards to a lighter hue.
The yellow colour in the upper stratum is considered by those far
more competent to judge than I, to be due to weathering. Mr.
Whitaker, with whom I had some correspondence on the subject of
water in the Boulder Clay, thus writes :—"As the difference between
the white upper part and the blue lower part of the Boulder Clay may
be due to a kind of surface action (alteration by very slow percola-
tion?) it is not improbable that water may be found in small
quantities at the junction of the two." But this view as to surface
action does not to my mind seem quite satisfactory, for in a newly
exposed section the contrast between the two clays at the junction
is so very marked that it has led me to believe they must have had
a slightly different origin.
I admit that although the two clays differ in colour, their compo-
sition is very nearly identical, but there seems to me to be a greater
admixture of Kimmeridge or Oxford Clay in the lower stratum than in