" They vary much in their exact nature in different
districts, but they universally consist of one, or all, of the
following members:--
1. _Unstratified_ clays, or loams, containing numerous angular
or sub-angular blocks of stone, which have often been transported
for a greater or less distance from their parent rock, and which
often exhibit polished, grooved, or striated surfaces. These
beds are what is called _Boulder-clay_, or _Till_.
2. Sands, gravels, and clays, often more or less regularly
_stratified_, but containing erratic blocks, often of large size,
and with their edges _unworn_, derived from considerable distances
from the place where they are now found. In these beds it is
not at all uncommon to find fossil shells; and these, though of
existing species, are generally of an Arctic character, comprising
a greater or less number of forms which are now exclusively found
in the icy waters of the Arctic seas. These beds are often spoken
of as "Stratified Drift."
3. _Stratified_ sands and gravels, in which the pebbles are _worn_
and rounded, and which have been produced by a rearrangement of
ordinary glacial beds by the sea. These beds are commonly known
as "Drift-gravels," or "Regenerated Drift".
Some of the last-mentioned of these are doubtless post-glacial;
but, in the absence of fossils, it is often impossible to arrive at
a positive opinion as to the precise age of superficial accumulations
of this nature.
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