204 R. S. TARR AND LAWRENCE MARTIN 
of the Copper River basin the till is buried beneath the outwash. 
Knobs and kettles, and lakes and swamps are abundant in the till 
areas. Kames and eskers are present, but thus far no one has 
found drumlins. 
Alternation of beds.—The alternation of silt and gravel with 
bowlder clay suggests either a complexity of the period of deglacia- 
tion, or else that pro-glacial outwash gravels, laid down by glacial 
streams in front of the advancing ice sheet, are to be identified 
below the till beds, with post-glacial outwash, from the retreating 
ice, above. Sharply folded structures in the stratified clays and 
silts show the effects of this overriding. Weathering has not 
been recognized in the lower beds, so that interglacial epochs 
are not yet suggested by the Alaskan drift. 
Volcanic complications.—Near the mountains the presence of 
lava flows, resting upon, and even intruded in, glacial deposits 
has been described by Schrader and Spencer,’ and the complica- 
tion of past and future ash showers upon the drift is suggested by 
volcanic ash in some parts of Alaska with thicknesses of a few inches 
to 75 or roo feet in an area of many hundred square miles. Present 
eruptions of Mt. Wrangell, as in April, 1911, show that this 
process may occur in the future, leaving volcanic ash beds upon 
or inter-stratified with the till, outwash, and vegetation of the 
Copper River valley. In at least one locality 35 miles from the 
nearest active volcano, Mt. Wrangell, enormous masses of angu- 
lar volcanic rock occur in blocks, buried in the outwash gravels 
and till beds, suggesting either volcanic showers of large bombs 
or material carried in glacial floods, as in Iceland. These 
volcanic fragments are abundantly exposed in 1910 and tg11r in 
cuts along the newly constructed railway, near Chitina. Other 
occurrences of the same sort are known, as much as 45 miles 
from Mt. Wrangell. 
Lake deposits.—Large areas of very flat topography with clayey 
soil suggest former, local, glacial lakes, and some of the sections 
reveal over 300 feet of fine silt with a few scattered stones, perhaps 
dropped by floating icebergs. In some sections, measured by 
«=F, C. Schrader and A. C. Spencer, House Doc. 546, 56th Cong., 2d sess. (1901), 
p. 59 and Pl. XI, A, facing p. 54. 
