1875.] Niagara. I4I 
of the Lake of Ontario, it had, in its progress south-west- 
ward, reached the base of the cliffs of the Queenstown 
escarpment, or had dammed back the water to that level, 
the commencement of the filling up of the old Niagara 
gorge was at hand, and from that time, during the advance 
of the ice and its subsequent retreat, the deposits of sand, till, 
and boulders shown in the sections were made. ~The first 
step was the partial arrest of the flow of the old river, 
causing it to deposit at a higher level than its original bed, 
first pebbles forming the conglomerate at the base of the 
section in fig. 1, and then the thick bed of river sand, when 
the current was still more impeded. ‘The bed of fine silt 
(B in fig. 1) marks the time when the flow of water to the 
north-east was completely stopped. Dr. Newberry, several 
years ago, first drew attention to the fact, that at some time 
during the glacial period, all the great lakes of North 
America drained towards the Ohio and the Mississippi, and 
since then, several deep channels by which they did so have 
been described. 
I did not see this fine bed of silt in any of the other sec- 
tions I examined, and I think its preservation in the one at 
the whirlpool must have been entirely due to the protection 
the nearly perpendicular walls of the gorge afforded against 
the great pressure of the ice that passed over it. Its upper 
portion contains small angular stones, and it gradually 
merges into the unstratified till, containing large angular 
blocks. 
It is probable that, during the advance of the ice, no till 
or grund morane was formed below it, but that the smooth- 
ing and scratching of the surfaces of the solid rocks were 
then effected, and that the till was deposited beneath the 
ice when it was melting back, and its pressure being gra- 
dually lessened. Mr. Bonney has objected to the theory of both 
the erosion of rock surfaces and the deposition of till having 
taken place below the ice.* But the two actions belong to 
different times ; the one was accomplished during the ad- 
vance, the other during the retreat of the ice. The effects 
are similar to those of a mountain torrent, which, when full, 
carries all before it, but which, when its waters lessen, 
deposits stones and mud in its course. During the advance 
of the ice, there could be little deposition below it, all the 
stones held at the bottom of the moving mass being pro- 
bably ground to powder; but, as it melted back, the stones 
and clay held within it would be deposited at its foot. 
* Nature, vol. x., p. 85. 
