Re: Ice Sheets

Arthur V. Chadwick (
Mon, 01 Dec 1997 16:08:39 -0800

At 04:23 PM 12/1/97 -0400, David wrote:
> It should not be hard to distinguish a true tillite from other ways
>of generating grossly poor sorting (large rocks and mud mixed together),
>based on the size of the deposit, source area of the clasts, shape of the
>clasts, cold-associated fossils, presence of other glacial features,
>glacial scratches on rocks, weathering of the clay minerals, etc. The
>identification of many deposits as glacial rather than Noachian flood in
>origin goes back to the mid-1800's, well before Darwin's publication.

Lots of pebbly mudstones interpreted as glacial have been traded out
subsequently, usually because of the unliklihood of glaciation at the
interval or locality of the deposit. The classical paper of Roger Walker
on this subject is a landmark.