80 NEW YORK STATE MUSEUM 
their headwaters farther southward, but only along belts of weak 
rock and in harmony with the northeast-southwest folded structure 
of the region. 
In a similar manner the great Mohawk valley has been developed. 
The Mohawk is the chief tributary of the Hudson, and whether or 
not its ancestor flowed in about the same position upon the surface 
of the peneplain, we do know that the present Mohawk valley 
(below Little Falls) has been carved out of the upraised peneplain 
by the Mohawk river and its tributaries along a belt of weak 
Ordovicic shales. The valley is bounded on the north by the very 
hard Precambric rocks and on the south by the fairly resistant 
limestones of the Helderberg escarpment. Proof will be given 
on a later page for the statement that late in the Tertiary (that 
is just prior to the great Ice age) the Mohawk river had its 
source near Little Falls, and that at the same time another stream 
(Rome river), now extinct, flowed westward from Little Falls, 
past Utica and Rome and into the basin now occupied by Lake 
Ontario. West Canada creek was then tributary to the Rome 
river, while the Sacandaga river flowed into the Mohawk instead 
of the Hudson as it now does. 
However uncertain we may be as to the location of a Precenozoic 
Susquehanna river, we are very certain that the present numerous, 
deep channels of the Susquehanna drainage system have been cut 
into the upraised peneplain. The Susquehanna, like the Hudson, 
is a good example of a superimposed stream and its ancestor may 
have flowed along the same general course over the low-lying pene- 
plain before its uplift. Immediately after the uplift some of the 
more easterly headwaters of the Susquehanna came out of the 
southern Adirondacks. Evidences of this are as follows: (1) The 
present Mohawk valley had not been formed, the Mohawk river 
then having only begun the westward migration of its headwaters 
along the belt of soft shales; (2) the natural slope of the southern 
Adirondack region was then southward into the east branches of 
the upper Susquehanna; and (3) the positions of the present 
sources of the east branches of the Susquehanna at the crest of 
the high Helderberg escarpment, and in some cases within a very 
few miles of the present Mohawk river (see drainage map, figure 
11) strongly argue for the cutting off or beheading of the former 
headwaters of the east branches. This beheading was accomplished 
by the Mohawk as its headwaters migrated slowly westward thus 
tapping one by one of the upper waters of the east branches of the 
Susquehanna. Even today the Mohawk continues to steal drainage 
