22
PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .MaV 17,
deposited simultaneously, or in a violent manner, as this is a common
character in all mud formations.
In the sections now exhibited, the brown clay rests on a pretty
even surface of the till. In some other places however there was
proof that the till had been exposed to erosive action before the de-
position of the immediately superior formation. In many places it
was worn into hollows, as if part of it had been removed by the action
of water : one of these hollows was very remarkable, being about five
or six feet wide by three or four deep, and closely resembled the
channel of a small stream. It was also filled with gravel and sand,
in all respects like that found in such a stream at present. It was
seen with the same characters on both sides of the cutting, but how
far it continued beyond could not be known. I had no doubt that
it had been formed by some stream of rummig water, which, if we
suppose the till deposited in the sea, would imply that it had been
elevated and again depressed for the deposit of the superior beds.
This elevation of the till to the surface, permitting the action of the
atmosphere on any shells or other remains contained in it, may
perhaps accomit for the rarity or rather entire absence of fossils in
this deposit.
The second subject which I should wish to notice has reference
to the transport of erratic blocks. As already stated, this has begun
even in the earliest period, during the deposition of the till, and has
continued down to the most recent. They occur in the brovra clay
represented in the sections resting on the till, and in a higher deposit
of gravel and boulders which often covers the deposit of fine strati-
fied sand seen filling a hollow in the brownii clay in section fig. 3.
Fig. 3.
Stratified sand.
They are frequently found lying completely exposed on the surface,
and in this case may never have been buried in any of the subjacent
deposits. Boulders of trap rocks are by far the most common, but
with them are many fragments of sandstone, limestone, and even of
coal, and a few also of primary rocks. I have found the latter over
every part of the coal-field, and far up the sides of the transition
mountains that bound it on the south : even in the centre of that