388 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
crevasses which may interrupt its continuity. Overriding, or even 
a local thickening of the ice, may not always accompany the cessa¬ 
tion of flow ; but it is certainly difficult to see how, in general, 
crevasses could survive the progressive loss of motion. We have a 
magnificent illustration of this process in the Malaspina glacier, 
which is practically free from crevasses and well endowed with 
persistent superglacial streams on its outer, drift-covered, marginal 
zone, although crevasses are a common feature of all the central and 
northern part of this great piedmont glacier, or at least common 
enough to prevent the development of any important superglacial 
streams; and we can only suppose that they are closed by pressure 
from the northward or clogged by superficial drift as the ice gradu¬ 
ally ceases to flow. In fact, Russell says that many of the crevasses 
are filled with clear blue water, and that they appear to be the 
scars left by rents in the tributary ice streams, indicating a tendency 
of the crevasses to close at the bottom before they do at the top. 
Concerning the drainage of the Malaspina glacier. Stone says (’99, 
p. 421-422), “For some reason the glacial streams have either 
formed no subglacial tunnels under a marginal zone of uncertain 
breadth, or the original tunnels have become blocked by ice or 
sediment or moraines so that the streams have been forced to form 
englacial tunnels, which become superglacial by the melting away of 
the overlying ice, and the streams continue such as they flow down 
the terminal ice slope. If the glacier continues to retreat, it seems 
probable that a ridge or series of ridges such as are now forming, 
and abandoned channels of these rivers will be prolonged northward 
as far as the englacial channels reach. This furnishes an observa¬ 
tional basis for the conclusion that during the retreat of the ice 
sheet, wherever the ice was very stagnant and the subglacial streams 
found their tunnels choked near their outlets, they freely rose into 
englacial or superglacial channels.” This is important testimony, 
and all the more interesting as coming from a subglacialist. Surely, 
if a piedmont glacier on a narrow, sloping, coastal plain, at the base 
of lofty mountains, with a steep frontal slope, and feeling the thrust 
of powerful alpine glaciers, can become absolutely stagnant and free 
from crevasses in a distance of only five to fifteen miles from the 
mountains, and while still retaining a thickness of a thousand 
feet or more, we need not doubt that the wasted margin of the 
Pleistocene ice sheet, on the vast, dissected, peneplain tracts of 
