238 The American Geologist. October, 1902. 
end, and fiirther.these streams sometimes contain silt which 
must have been raised from the bottom of the glacier. 
Stratification. 
Some observations on the stratification of glaciers have 
been made, though it is said that a correct observation of this 
phenomenon is very difficult. Prof. Heim* gives some atten- 
tion to stratification, and Prof. H. F. Reid also gives a theory 
concerning it. t He says, "In order that the general volume 
of the glacier should be preserved we must have below the 
neve-line, where there is melting, a component of the motion 
toward the surface, and this component is strongest where the 
melting is greatest ; i. e., it gets larger as we descend the 
■dissipator. Above the neve-line this is reversed." The move- 
ment of a glacier is so related to its formation and surroundings 
that stratification is probable, though it seems that a thin 
layer of debris is almost absolutely necessary to determine 
the surfaces of separation. 
Drawings made by Agassiz show such layers as he found 
them in the Unteraar glacier % and they appear to be true 
surfaces of stratification. In some instances it is observed 
that rock material falling upon the snow in the cirque is car- 
ried along the under part of the glacier, reappearing at the 
■surface near the terminus. Debris layers in the Sierra Nevada 
g-laciers are cited by Prof. Russell § as separating successive 
strata. 'The parts of strata formed at a distance from rocky 
slopes have very little dust blown upon them, and consequent- 
ly when they reappear at the surface in the upper regions of the 
■dissipator the stratification is but slightly, if at all, indicated 
by dust bands. The strata should be well defined at the lower 
end, but the large amount of debris on the surface and in the 
crevasses, would make them difficult to recognize." || 
A controversy existed between Agassiz and Forbes in 1841, 
as to the meaning of banded structure seen on the surface of 
glaciers. The former contending that such structure marks 
the outcrop of strata, while the latter believed it to be a 
peculiarity of glacier ice, and independent of stratification. 
*Gletscherkunde. 
tJour. of Geology, 1896, Vol. 4, pp. 917 to 923. 
JSysteme Glaciare, p. 260, Atlas, plate 5. 
§Tlie glaciers of U. S. 5th Ann Rep. U. S. Geol. Surv. 1883-4. 
li Mechanics of Glaciers. H. F. Reid. Jour, of Geol. 1896. Vol. 4. 
