#Fold mountains
<<I'd think that if erosion proceeds to the point of actually flattening out
the countryside and the area is then uplifted again, new drainage patterns will
develop away from the center of the uplift. There may certainly be traces of
the former drainage pattern.>>
Yes, certainly. The eroding folds and faults remain the determining factors in
the topography of the central and southern Appalachians. And my point was that
they always will be the determining factors until they themselves are buried
with sediment.
<<I really can't see any hard evidence that the Applachians are older than the
Early Cretaceous.>>
No big argument here either, just a qualification that the several orogenies
we've discussed here which formed the mountain chain apparently proceeded from
north to south over time. Devonian beds are clearly involved in the folding in
northeast PA and southern New York, and these had to have come from an earlier
event northward and eastward. Jon Wolff described the individual events in
excellent order in an earlier message. In another previous post I said I was
pretty sure that the Permian beds which begin in extreme southwest PA just west
of the first discernible Appalachian upfolds lay conformably atop the
Pennsylvanian. If that IS true, it puts the major orogeny along that section of
the chain at least into the early Mesozoic. Sorry I'm not good for much
information on the eastern flank of the range. I figured the Triassic and
Jurassic in the rifts was deposition of sediments washing down off these ranges
as the Atlantic started to open up, but haven't seen enough of that area to be
able to say with any certainty.