466 
Prof. Milne — Across Europe ancl Asia. 
new ones might be born. Not overlooking the observations of Pro- 
fessor Agassiz on the Amazons, and those of Mr. Belt in Nicaragua, 
evidences of this kind are yet very rare. As additional reasons for 
not forming too liasty a conclusion, we must wait until the markings 
of the ice-cap have been shown to be more general in their dis- 
tribution, and the markings which would be consequent on such a 
covering have been more fully recognized. Cosmical changes have 
no doubt produced their effect upon climate, and so also have causes 
like those we now see in action, and therefore I do not see the 
necessity that all glacial phenomena should be attributed wholly to 
the one or to tlie other cause ; but I must confess that where it is 
possible to adopt existing agencies, I should take them into con- 
sideration hefore those whose origin and subsequent mode of action 
was of a more debatable character. For these reasons, together 
with the fact that the Siberian Steppes present phenomena not well 
explained by the invasion of a polar ice-cap, I venture to suggest 
a modification of the theory advocated by Mr. Belt and Siberian 
geologists, which appears to me to be more reconcilable with the 
phenomena which have been hitherto recorded. 
In addition to the general freshwater character of the plains which 
has been already noticed, we must also observe the slight elevation 
which they have above the Northern Ocean towards which their 
rivers flow. On physical maps points more than 1000 miles inland 
are shown not to be more than 250 feet above it. Another point 
to be observed is that the last movement which these plains have 
made, as indicated by beds of marine shells along their northern 
frontier, has been an upward one. From tliis we may infer that 
when they were at lower levels a considerable portion of their 
surface must have been covered by what would now be an invading 
sea. At such a time the rivers would be shorter in length, and the 
plains, through which they flow, more tongue-like in their character. 
Again, we must observe that in old times, as at the present day, 
these rivers were often covered with ice, which, blocking up their 
channels, may have given rise to floods. These actions can now 
be seen both at the forming and the breaking up of these winter 
barriers. By comparison with what has liappened in Europe and 
in America, we may infer that either cosmical or geographical 
changes, or perhaps both, have in former times intensified this 
action. 
The following table, which I have compiled from information 
collected when in Siberia, will show approximately the time of 
formation and breaking up of ice at different latitudes upon the satne 
and different North Asian rivers, and will indicate an important 
cause operating in the formation of these floods or temporary lakes : 
The first thing that will be observed in this table is that the 
influence of latitude practically outweighs all local circumstances 
which might accelerate or retard the time of freezing, or the break- 
ing up of the ice upon these rivers. The farther north a place is, 
the sooner the water freezes, and the later is the ice broken up, as 
compared with more Southern positions. Another point to be noticed 
