Thanks, everyone.  Interesting reading.  From what I know now it still
seems like much remains to be understood.  In the case of the
Appalachians, it seems people are agreed that they were pushed up by the
collision of tectonic plates, the North American, African and European
plates colliding ~ 500 million years ago.  I don't know which plate(s)
went below and which ended up on top, but the Appalachians were once among
the mightiest mountains on earth, perhaps higher than the Himalayas.  The
mountains of Ireland, Scotland, and the north of England are part of the
same system, which ends with the Harz mountains of Germany.  The wide
separation between these mountains today is due to continental drift since
the original uplift event.  I was expecting a similar explanation for the
Adirondacks.  But it seems as if tectonic plate collisions were not
involved.  The pages people posted are more detailed on the events that
have sculpted these mountains than they are on the original uplift

There is a large field of planetary geologists that I never knew existed
until I joined NASA.  It is astonishing what these people will conclude
from what seems like the flimsiest of evidence.  (I am trained in chemical
kinetics and spectroscopy.)  Still when one questions them vigorously the
thought processes behind their hypotheses are impressive.  It's
fascinating stuff.

Hope I haven't bored anybody to excess.  After all it is Sep. and I have
sworn not to get into politics or baseball.

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