"1184 The American Naturalist. [December, 
appears to be an intermediate or transitional formation (hence the 
name Transitional Drift which I have applied) between the true Drift 
below and the Loess, which occupies a chronological horizon above. 
If I discern correctly, the Transitional Drift is distinguishable from 
true Drift (1) by the almost entire absence of clay; (2) the relatively 
small amount of gravel and bowlders ; (3) by the looseness and more 
homogeneous nature of its earthy base; and (4) by its stratigraphical 
position and color, It is also distinguished from Loess mainly by its 
looseness, color, almost absence of clay, and less homogeneous charac- 
ter, as well as by its containing both gravel and bowlderettes.* 
It is not infrequently the case that the constituent elements compos- 
ing the true Drift and the Transitional Drift pass into one another 
with such gradual and imperceptible gradation as to make it impossible 
to designate just where the division line separating the two formations 
should be drawn. At other times, however, the line of demarkation 
or separation between the two sheets is abrupt and sharply defined. 
The material of the Transitional Drift is also sometimes seen to so 
imperceptibly graduate into the Loess as to make it a hopeless task to 
undertake to indicate just where the line separating the two deposits 
should be placed 
It is believed that the component elements of this formation were 
derived mainly from the less coarse material contained within the 
glacial ice, which material, upon the melting of the ice, was dis- 
tributed, with more or less uniformity, by its waters over large areas 
covered by the Drift, which had accumulated under the glacier. 
It is manifest, upon consideration, that the finer material held in 
suspension by the glacial waters would not settle down so soon as the 
coarser material forming the Transitional Drift, but would be borne 
along by the more or less rapidly-moving floods, and finally be depos- 
‘ited in the form of sediment as the waters collected and formed into 
lake-like expansions along the axis of drainage. 
This sediment we conceive to be our typical Loess, which we 
believe to be analogous to the Transitional Drift, only modified by 
* Prof. Torrell has distinguished a Drift sheet, apparently somewhat similar to this, in 
the hilly regions of Eastern America (it is also recognized in Sweden), which has been 
ted ‘‘ Upper Till.” 
“ It is held to be distinguished from true Till (r) by its looseness; (2) by the pone! 
large size and angular form of its rock fragments; (3) by the more sandy and porous 
character of the hnic d base ; and Q by the higher oxidation of: its ion compound” 
jal ice 
Lig e i PY 
on its surface, and by its meiting let loosely down upon the true Till formed beneath the 
ice."— 7. C. Chamberlin, U. S. Geological Report, r881-'82, p. 297. 
