356 Dr. J. Croll on the Ice of 
occupy 4 square feet, and at latitude 60° the space covered 
will be 6 square feet. Then if the layer was i foot thick at 
latitude 85°, it would be only 6 inches thick at latitude 80°, 
3 inches thick at latitude 70°, and 2 inches at latitude 60°. 
Had the square foot of ice come from latitude 89° it would 
occupy 30 square feet by the time it reached latitude 60°, and 
its thickness would be reduced to 4 C) of a foot, or § of an inch. 
Now the lower the layer the older it is, and the greater 
the distance which it has travelled. A layer near the bottom 
may have been travelling from the Pole for the past 10,000 
or 15,000 years, whereas a layer near the top may perhaps 
not be 20 years old, and may not have travelled the distance 
of a mile. The ice at the bottom of a berg may have come 
from near the Pole, whereas the ice at the top may not have 
travelled 100 yards. 
There is still another consideration which must be taken 
into account. It is this : the icebergs all seem to bear the 
mark of their original structure, and the horizontal stratifica- 
tions appear also never to have been materially altered in their 
passage from the interior. This fact seems to have struck 
Sir Wyville forcibly. "I never saw." he says, "a single 
instance of deviation from the horizontal and symmetrical 
stratification which could in any way be referred to original 
structure ; which could not, in fact, be at once accounted 
for by changes which we had an opportunity of observing 
taking place in the icebergs. There was not, so far as we 
could see, in any iceberg the slightest trace of structure 
stamped upon the ice in passing down a valley, or during its 
passage over roches moiitonnees or any other form of uneven 
land ; the only structure except the parallel stratifications 
which we ever observed which could be regarded as bearing 
upon the mode of original formation of the ice-mass, was an 
occasional local thinning-out of some of the layers and thicken- 
ing of others, just such an appearance as might be expected 
to result from the occasional drifting of large beds of snow 
before they have time to become consolidated." 
There cannot, I think, be the shadow of a doubt that these 
thin horizontal bands of clear blue ice, with their less dense 
and white intervening beds, are the original structure of the 
bergs. And it is evident that if the ice had crossed mountain- 
ridges, valleys, or other obstructions in the course of its 
journey from the interior, these beds cculd not have avoided 
being crushed, fractured, broken up, and mixed together. 
Had this happened, it would have been physically impossible 
that they could ever have' been restored to their old positions. 
Ice is, no doubt, plastic, and pressure, along with motion, 
