S. V. Woocl,jun. — American and Br Hink Surf ace- Geolog y. 495 
these marine clays belong to a later glaciation than tbat to which 
the Erie clay owes its origin ; because I cannot, as I have already 
observed, conceive tbat with such vast erosive power as is attributed 
to glacier-ice any deposits of prior Glacial age could survive its 
destructive agency, so far as it extended. In the case of the older 
Glacial beds of East Anglia they remain undestroyed, it seems to 
me, only so far as the subsequent ice giving rise to the Middle and 
Upper Glacial formation did not extend. The depth of the water 
under which the Lower Glacial of East Anglia accumulated renders 
it difficult to conceive that this formation did not extend north and 
west of the limits to which it is now restric-ted ; and it must have 
extended either in a marine or terrestrial form as far northwards 
as the ice to which it owed its origin wasted back or deflected ; so 
that when we combine the absence of any formation representing it 
in the North of England with the Crag-like character of the mollusca 
of its basement sands, it seems but reasonable to regard this earlier 
part of the Glacial series as having been largely destroyed by the 
subsequent advance upon it of the ice. 1 Now there is an absence 
from the marine clays of the Lower St. Lawrence basin, and of the 
Atlantic coast, of any species of mollusca but such as still occur in 
a living state either in the Atlantic or in the Arctic sea immediately 
north of it, 2 while there are Crag forms in the English older Glacial 
beds, which are not known as living at all ; and othei-s, which, 
if living, are only represented by species known as such in 
the North Pacific; and two of these, as, e.g. Nucula Cobboldice, and 
Tellina obliqua, ränge in our Upper Glacial clay up to what I regard 
as about the middle place in its horizontal accumulation, viz. 
Dimlington Cliff base, and Bridlington. This leads me to think 
that the marine clays of the Lower St. Lawrence and of the Atlantic 
coast were deposited during the time of the later or minor ice-sheet 
which gave rise to the beds 3a of Ohio. Mr. Geikie also in his 
second edition refers these clays to the later part of the Glacial 
period as defined by him, which corresponds with what I call post- 
Glacial. 
Besides the beds above described, and those yet to be mentioned 
under the number 4, there is the great Bluff formation or Loess of 
the Mississippi valley, described by Sir Charles Lyell in the succes- 
sive editions of his well-known works, and in which at Natchez he 
mentions the occurrence of a human pelvis. 
This formation Prof. Newberry regards as the silt brought down 
by the rivers which form the Mississippi drainage System when in 
flood, and spread out over the great valley as the sea by the eleva- 
tion of the continent receded from it, the chief contributor being the 
Missouri with its affluents. There is, he says, evidence that the 
lower part of the valley near New Orleans was depressed nearly 
1 The line up to which this formation, and also the Middle Glacial and earliest 
part of the Upper, have been destroyed by the subsequent ice is defined in a note to 
the sequel of this paper. 
2 This, at least, is my impression, from the works to which I have had access. If 
the facts are otherwise, then my argument to that extent fails. 
