GLACIAL DEPOSITS OF THE CONTINENTAL TYPE 207 
decomposition of the mineral particles, which are exceedingly 
angular. Their size varies from .03 to .5 millimeters. 
As the loess from the Mississippi Valley averages under 0.0025 
to .oo5 millimeters in diameter,’ and the maximum size rarely 
exceeds 0.11 millimeters it is apparent that there must be special 
reasons why these eolian deposits from the Copper River valley 
in Alaska are exceptionally coarse. The unusual conditions of 
deposition of this coarse Alaskan accumulations are explained later 
(p. 300). 
Topography.—The topography of this eolian silt is smooth, 
molded to the underlying bedrock or drift topography, and never 
dune-like. The exposures show typical steep clifis, where cut into 
by streams and by railway grades. There are many vertical joints 
and the exposure is, therefore, much like those of the loess in the 
Mississippi Valley and in other localities in the Middle West. 
Thickness of deposits —The thickness is from a few feet to 4o 
or 50 feet, and in one case 80 feet. Some of the deeper cuts do 
not reach the bottom of the deposit. In a few places the bottom 
of the loess soil is revealed as a sharp contact with glacial outwash 
gravel or till. 
Fossils —Shells of terrestrial? animals are abundant in the 
exposures, and their presence 20 to 40 feet below the surface and 
back several feet from the faces of cuts in recent railway excavations 
is clear evidence that these are the fossils of animals which lived 
during the period of accumulation of the deposits. 
Vegetation.—The included vegetation is well-preserved wood 
in minute fragments and good-sized logs (Fig. 3). There are also 
upright stumps of trees, up to a foot in diameter and in some of 
the thicker deposits those are found in layers several feet apart 
and one above the other. The greatest number of layers of stumps 
that we have seen was 7, and as these stumps were all clearly 
in place, it may be assumed that the wind-blown deposit has 
accumulated during the time necessary for the growth of 7 
generations of trees. The present forest upon the loess surface is 
thick and mature (Fig. 4). Many of the modern trees are 11 to 
tT, C. Chamberlin and R. D. Salisbury, 6th Ann. Rept., U.S. Geol. Survey 
(1885), pp. 279-80. 
2 Collected in 1911 and determined by Professor B. Shimek. 
