MORAINES OF RECESSION 439 
western Ohio, in Indiana, and Illinois are of Canadian origin, 
and nearly all are of the hardest crystalline varieties. Consid- 
ering the dominant englacial mode of transportation, the contin- 
ual and very complicated changes in the direction of glacial 
flow and the dispersion from the lobate axes, it becomes 
extremely difficult, if not altogether impossible, to account for the 
bowlder belts except by the intervention of some later agency 
of bowlder concentration—some agency that operated near 
where the bowlder belts are now found. It seems impossible 
that any marked bowlder belt could have been brought all the 
way from Canada with the bowlders in such close relationship as 
that in which they now lie. Some of the bowlder belts of 
southwestern Ohio, southeastern and western Indiana are very 
pronounced in their development. It is conceivable that they 
might have been formed by the marginal concentration of super- 
glacial or englacial bowlder trains, but it is hard to think of 
those trains as coming directly all the way from Canada." The 
distribution of bowlder belts is peculiar and indicates that 
the conditions of their production are exceptional. One 
moraine may show a well-formed bowlder belt, while its neigh- 
bors parallel with it in front and behind have none. The diverse 
composition of the bowlders seems also to be against the idea 
of concentrated bowlder trains. In short, it would seem that we 
must look much nearer than Canada for the cause of their very 
local concentration. The only local cause that seems available 
grows out of the relation of the readvancing ice-front to power- 
ful lines of drainage at or near the edge of the ice. If, during 
the building of a terminal moraine, a powerful stream of water 
sweeps past the front of the ice so as to carry away the finer 
material the bowlders may be left on the surface in greater num 
bers than usual. Several of the well-known abandoned outlets 
have more or less of this appearance. But where this is the 
whole process the bowlders remain in a low position with respect 
to the surrounding lands. If, however, a readvance of the ice 
*“ Bowlder Belts Distinguished from Bowlder Trains—their Origin and Signifi- 
cance,” by T. C. CHAMBERLIN. Bull. G. S. A., Vol. I, 1890, pp. 27-31. 
