Great Ice- Dams. — Taylor. 35 
Co?icliision. 
If the moraines mark halting places of the barrier and are 
to be accounted for in a manner accordant with their observed 
relations to the beaches and outlet channels, then there is only 
one order for the making of the series. Generally speaking, the 
barrier must always have faced southward and covered the 
lands to the north, and not vice versa; for the beaches and out- 
lets could not be explained by a contrary supposition. Xeither 
can we suppose the moraines to have been made all at once, 
nor in successive order from north to south, nor irregularly. 
They must have been made in series from south to north, for 
no other supposition puts the barrier into proper relations to 
the beaches and outlets. 
The relation of the several moraines in the order of their 
series to the topography indicates a barrier composed of ma- 
terial in some degree mobile and plastic and moving in a south- 
erly direction from the lake basins, which it must have filled 
solidly, not only to altitudes somewhat higher than the corre- 
lated beaches and outlets, but up to the hight of the highest 
parts of the observed moraines. These conclusions might have 
been reached without any knowledge of the real composition 
of the barrier, for they are all clearly indicated by the close 
interrelations of the beaches, outlets and moraines indepen- 
dently of the Glacial theory. But with the Glacial theory and 
the verity of the continental ice-sheet firmly established on a 
basis of facts which have no dependence upon shore lines and 
outlets for their interpretation, an explanation is at hand so 
clear and comprehensive and introducing so high a degree of 
unity and harmony among the many facts relating to the tem- 
porary lakes of the Great Lake region that no tenable ground 
eye than the Ubiy channel. In this case a glacial lobe retreated down 
a partly dissected hii^hland slope or escarpment and finally opened an 
outlet along its front directly across ridges and valleys. The backs 
of the ridges were cut through by the river and deltas were built in 
the intervening valleys. Some of the ridges were cut several times 
at successively lower levels. The general surface slopes rapidly down- 
ward to the north, while the channels run from west to east. The 
situation is such that the front of the ice-sheet must be supposed to 
have stood just there beside the channels while they were being made. 
There appears to be no possible alternative explanation of their origin. 
(Gilbert, abstract in Bull. G. S. A., vol. 8. 1896. Fairchild, in Bull. 
G. S. A., vol. 10, i8g8, with maps and photographic views. Quereau. 
an account of Jamesville Lake, N. Y., Bull. G. S. A., vol. g, 1897.) 
