SINUWIDIMES PHONG SIQUDIGIN TES. 85 
valley, while any one may predominate over all the others else- 
where. In its physical heterogeneity therefore, this stony glacial 
débris very closely resembles certain common phases of our 
continental drift. In the glacier deposits of mountain valleys, 
however, stony material is likely to be more abundant relatively 
than in our drift. 
If the stones of the drift in glacier valleys be examined, a 
considerable variety of rock types may sometimes be found. 
The glacier deposits are thus seen to possess lithological, as well 
as physical, heterogeneity. This isa second point of correspond- 
ence between glacier deposits and the drift. If the stones in 
glacier deposits be studied in connection with the surrounding 
rock formations which are zm situz, it is found that the stony 
material deposited at the foot of any particular glacier corresponds 
with the types of rock found along the course of the valley 
through which the ice has come, and further, that pieces of all 
types of rock represented in the course of the valley through 
which the ice has come, are liable to be found in the deposits left 
by the ice on the surface from which it has withdrawn. But in 
general, the lithological heterogeneity in the deposits of existing 
glaciers is less extreme than in our drift. 
In the glacier deposits, the various constituents, ranging from 
huge bowlders to fine clay, may often be seen mingled together 
without trace of stratification, just as in our drift. But stratified 
deposits are by no means wanting. Beds of assorted sand and 
gravel may sometimes be seen to overlie unstratified mixtures 
of bowlders, gravel, and clay in some places, and to underlie 
similar materials in others. Beds of stratified material may even 
be inserted between beds of unstratified. In all these character- 
istics and relations the deposits of the glaciers resemble those of 
the drift. 
Many of the stones of the unstratified glacier deposits possess 
the subangular forms, and the planed and beveled surfaces which 
have been noted as characterizing the stones of our drift. The 
stony material of the stratified drift associated with glaciers is 
more commonly rounded. Some of the stones left by the glacier, 
