20 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
tortion would appear to indicate smaller and smaller icebergs, for it is evident 
that a large berg would create more disturbance in the layers than a small one. 
Progressively smaller bergs might indicate a retreating ice front. The farther 
away the ice the smaller the bergs would be, on account of melting. On the 
other hand, the depth of water would determine the size of berg which could 
be floated at a given place and time, thus a change in the water level might be 
the controlling factor. What is to decide which factor controlled the size of 
the bergs which contorted these layers? A study of the thicknesses and char- 
acter of the annual deposits may possibly throw some light on this question. 
The lowest annual deposits visible in this section average one fourth of an inch 
in thickness. Upward, this thickness increases and just below the deposit 
of rock-flour and pebbles (No. 2) the thicknesses of the annual deposits average 
one half of an inch. In the group of bands numbered 7, the thickness reaches 
three fourths of an inch to each couple. Until the upper part of group (No. 22) 
is reached, the thicknesses of the units do not vary to any great extent, averag- 
ing one half inch, and these are one fourth inch thick. The constancy of the 
thicknesses of the annual deposits during this whole period of not less than 
1,100 years would appear to indicate that the ice was not many miles away 
when the deposits were made, and that it did not at any time retreat so far as 
to cause the bergs to be reduced in size to the extent indicated by the decreas- 
ing thicknesses of the contorted zones. A change in the depth of the water, 
to shallower conditions, might be indicated by the thinning of the contorted 
zones. The gradual filling of the basin of deposition with deposits would, other 
things being equal, decrease the depth of water. If to this should be added 
an elevation of the land the depth of the water would be still further decreased. 
Tarr, 1909, has given a good description of the calving of bergs from the 
_ Hubbard glacier of Alaska. In connection with this subject it is appropriate 
to quote his own words: 
“The discharge of a great many icebergs was witnessed, some of them from excellent 
points of observation near at hand. Far the greater number of the falls consisted of a crum- 
bling of the crevassed ice above the water level, giving rise to ice cascades, at a distance 
resembling falling water. Such discharges produce very small fragments. In other cases 
large masses fell forward from the ice cliff, producing great commotion in the water near the 
glacier front. 
“Occasionally masses of ice rose from beneath the water at a considerable distance 
from the ice front. Russell describes the latter condition and postulates a projecting ice 
foot extending fully a thousand feet in front of the ice cliffs. He gives a graphic description 
of the formation of such icebergs, which are sometimes 200 to 300 feet in diameter, and 
usually much larger than those falling from the face of the cliffs. Some of these large ice- 
bergs rise 40 to 50 feet above the water. 
