Exploring Visits to the Sources of the Hudson. 313 
Phenomena of Mountain Slides. 
A portion es the deep and narrow valley i in which we were now 
encamped, is occupied by a longitudinal ridge consisting of boulders 
and other debris, the materials, evidently, of a tremendous slide or - 
avalanche, which at some unknown period has descended from the 
mountain; the momentum of the mass in its descent having accu- 
mulated and pushed forward the ridge, after the manner of the late 
slide at Troy, beyond the center of the valley or gorge into which it 
is discharged. It appears indeed that the local configuration of sur- 
face in these mountain valleys, except where the rock is in place, 
ought to be ascribed chiefly to such causes. It seems apparent, 
also, that the Hudson, at the termination of its descent from the 
High Valley, once discharged itself into Lake Colden, the latter ex- 
tending southward at that period to the outlet of the Still Water, 
which has been noticed in our account of the former exploration. 
This portion of the ancient bed of the lake has not only been filled 
and the bed of the stream as well as the remaining surface of the 
lake, raised above the former level, but a portion of the finer debris 
brought down by the main stream, has flowed northwardly into the 
present lake and filled all its southern portions with a solid and ex- 
tensive shoal, which is now fordable at a low stage of the water. 
The fall of heavy slides from the mountains appears also to have 
separated Avalanche Lake from Lake Colden, of which it once form- 
ed a part, and so vast is the deposit from these slides as to have rais- 
ed the former lake about eighty feet above the surface of the latter. 
In cases where these slides have been extensive, and rapid in their 
descent, large hillocks or protuberances are formed in the valleys; 
and the denudation from above, together with the accumulation be- 
jow, tends gradually to diminish the extent and frequency of their 
occurrence. But the slides still recur, and their pathway may often 
be perceived in the glitter of the naked rock, which is laid bare in 
their course from the summit of the mountain towards its base, and 
these traces constitute one of the most striking features in the moun- 
tain scenery of this region. 
Main Source of the Hudson.—Fall of the Au Sable. 
On the morning of the fifth we found that ice had formed in ex- 
posed situations. At an early hour we resumed our ascending course 
to the southeast, the stream rapidly diminishing and at length becom- 
