British Association Reports. 561 
be abundant, from the greater room, and also an interchange from 
subsequent redistribution. 
I do not enter upon the great question of synchronism in parallel 
lines of disturbance suggested by Elie de Beaumont. The proba- 
bility of its truth is too evident; but I call particular attention to 
the great N. and S. lines of fissure, which I am convinced have re- 
ference to a much larger area than Wales. 
IJ.—Norzs on THE Post-pxiocens Depostrs or Canapa. By J. W. Dawson, 
LL.D., F.R.S., F.G.S. 
ART J.—On tHe Revative Acks anp Move or Formation 
OE THE SEVERAL MEMBERS OF THE POST-PLIOCENE SERIES.— 
The marine Post-pliocene deposits of Lower Canada are, in descend- 
ing order :— 
1. The superficial sands and gravels, called by the author the 
‘ Saxicava-sand.’ 
2. The underlying clay, named the ‘ Leda-clay,’ otherwise known 
as the Champlain-clay. 
3. The Boulder-clay. 
These beds extend over a very large area, and rise to the height 
of 500 feet in the valley of the St. Lawrence. The author gives 
short descriptions of each of them. The Saxicava-sand is a shallow- 
water deposit, presenting the appearance of a succession of beaches 
and terraces; it has been much modified by marine and sub-aérial 
denudation. ‘The Leda-clay is principally composed of material de- 
rived from the waste of the gray and red shales of the ‘Quebec 
Group ; its characteristic fossil is Leda truncata, an Arctic shell not 
now inhabiting the Gulf of St. Lawrence. The Boulder-clay is 
associated with these deposits throughout their whole extent, and 
Dr. Dawson believes that it is not a continuous stratum occupying a 
special place in the Post-pliocene formation, but that it is entirely 
a marine deposit, indicating the local action of floating ice, and that 
its accumulation has been proceeding throughout the whole of the 
period of the Leda-clay and Saxicava-sand down to the present 
time. 
Dr. Dawson gives examples of what he considers to be boulder 
deposits of different ages in Canada, which he classifies as fol- 
lows :— 
1. Boulder-drift anterior to the Deposit of the Leda-clay.—This 
contains fragments of Silurian and Laurentian rocks, and boulders 
often scratched and polished, and passes upwards into the Leda-clay 
at Montreal. 
2. Boulder-drift coéval with. the Leda-clay.—The Leda-clay, 
usually very fine and regularly stratified, occasionally contains large 
boulders presenting the appearance of having been dropped in, 
while it was accumulating, by melting ice, and subsequently buried. 
3. Boulder-drift of the Period of the Saxicava-sand.—Though 
the Saxicava-sand is a littoral bed, and was formed in much shal- 
lower water than the preceding, yet it contains many boulders pro- 
VOL. II.—NO. XVIII. ORO 
