, <a nare reree iin . a Se ee 
€ process 
howd has probably been heretofore e 
Gen. Totten on the Disappearance of Ice in Northern Lakes. 368 
paces be- 
tween the prisms, dissolves them out to the full depth to which 
the ice is immersed, and perhaps still farther, by capillary action. 
At the same time, the spongy ice, formed upon the upper surface 
by melted and refrozen snow, affords warm water, by melting 
and percolation, to affect similarly the porous spaces between the 
tops of the prisms. 
In this way, during the considerable period intervening be- 
tween the first spring rains and the final breaking up of the lake, 
the solid ice is transformed into the condition necessary to a sud- 
den dissolution. 
Ve may assume, indeed, that the solvent action begins on the 
lower surface, about the time the accretion, by farther freezing, 
ceases; that it proceeds very slowly, so long as the temperature 
of the water remains below that of the greatest density, and of 
course that it goes on more rapidly as the water is lifted above 
that temperature by the growing warmth of spring. 3 
I regret that I did not take the temperature of the water in 
the morning after the disappearance of the ice; but on this point 
I may add to what is said above, that the spring was then well 
forward, all, or nearly all, the snow had melted from the fields; 
the early rains and melted snows had for some time been raising 
the lake, which was then nearly at its greatest height. It was 
this rise in the lake that had spread a margin of water that did 
not freeze between the great field of ice and the shore. The in- 
ference from all the circumstances, that the temperature of the 
water at the time of disruption, and for some time previous, was 
not only above the melting point, but also above that of maxi- 
mum density, seems to me unavoidable. : 
I may here be permitted to mention another matter connected 
With fields of lake-ice that has excited some wonder, namely, the 
movement towards the shore of boulders, sometimes quite 1a1 
Th which must have occurred to intelligent o 
plained, seems to be this: 
the rising of the water has supplied an w en m 
a strong and wl comets ume the whole field to move 
until its edge meets adequate resistance upon the shore, all 
boulders encountered ae way, being pushed before it, into 
an array upon the shore that accurately marks the extent of the 
