72 
PALAEONTOLOGY OF NEW-YORK. 
denuding action. Thus the anticlinals are often worn down to such an 
extent as to form low grounds or deep valleys; while the synclinal, 
protected in the downward curving of the beds, remains to form the 
prominent mountain crest. This is very generally true in many parts 
of the Appalachian range; and it is only where some heavier or stronger 
bedded rock occurs, protecting the anticlinals, that they form the higher 
mountain elevations. Similar features will be observed in other moun¬ 
tain ranges*. 
It nowhere appears that this folding or plication has contributed to 
the altitude of the mountains : on the other hand, as I think can be 
shown, the more extreme this plication, the more it will conduce to the 
general degradation of the mass, whenever subjected to denuding agen¬ 
cies. The number and abruptness of the foldings will depend upon the 
width of the zone which is depressed, and the depth of the depression, 
which is itself dependent on the amount of accumulation. 
We have, therefore, this other element of depression to consider, 
when we compare mountain elevations with the thickness of the origi¬ 
nal deposition. 
It is possible that the suggestion may be made, that if the folding 
and plication be the result of a sinking or depression of the mass, 
then these wrinkles would be removed on the subsequent elevation; 
and the beds might assume, in a degree at least, their original position. 
But this is not the mode of elevation. The elevation has been one of 
continental, and not of local origin; and there is no more evidence of 
local elevation along the Appalachian chain, than there is along the 
plateau in the west. As it is, a large mass of the matter constituting 
the sediments of this mountain range still remain below the sea level, 
as a necessary consequence of the great accumulation ; while in the 
* The sections of the Geological Survey of Great Britain exhibit numerous examples of this kind. On 
the geological map of Great Britain, a section across the country presents us with Snowden summit as a 
synclinal, the height of which is much less than the thickness of the strata from the Longmynd to the 
Caradoc ; while, had the bedded trap of Moel Wyn and Aran Mowddwy, and its superincumbent strata, 
been sufficiently strong to have resisted denudation, the anticlinal axis would have presented a mountain 
far higher than Snowden. 
