60 NEW YORK STATE MUSEUM 
very existence is due to the fact that, as a result of the folding and 
subsequent erosion, the great sheet of hard and resistant conglom- 
erate has been left as a protective cap over the soft Hudson river 
(Ordovicic) shales (see figure 19). In the Rosendale cement 
region the effects of the folding are also evident (see figure 10 and 
plate 33). The folds in the Siluric and Devonic strata of Skunne- 
munk mountain were also produced at this time. Of course the 
whole lower Hudson valley was subjected to this mild compressive 
force but, since all the rocks older than the Siluric were already 
so greatly disturbed, it is often impossible to see the effects of the 
Appalachian disturbance. Thus we see that mountain-building 
forces have affected the rocks of the Highlands-of-the-Hudson at 
least three times (Precambric, Taconic revolution, and Appalachian 
revolution) ; Cambric and Ordovicic strata of the lower Hudson 
valley twice (Taconic and Appalachian revolutions); and the 
Siluric and Devonic strata but once (Appalachian revolution). 
The extensive faulting or fracturing of the eastern Adirondack 
and Mohawk valley regions is a matter of no small importance in 
our discussion of the physical history of the State, because the 
present major topographic features of those regions are largely 
dependent upon the faulting. It is generally believed that much 
of this faulting occurred toward the close of the Paleozoic era, and 
most likely at the time of the Appalachian revolution, but since 
considerable faulting certainly occurred later than that time, it is 
thought best to discuss this whole subject toward the close of the 
next chapter. 
