_ waves. Sand and pebbles were again formed, 
1056 The Materials of the Appalachians. | [Dec, 
_ seems to me that in this great conglomerate mass we have a 
record of a lost quartz-ridge or reef that existed in Middle Si- 
lurian days, but which long ago disappeared,—a reef of rock 
like that which now forms the ledges of the South Mountains; 
a ridge large and enduring enough to furnish all the sand and 
pebbles required, though the Medina is, in some places, two 
thousand feet thick. 
Nor is the existence of such a lost ridge along the Atlantic 
sea-board altogether imaginary. We know that in later days @ 
force has acted in the same region that was fully capable of pro- 
ducing such a result; and we have no reason to assume that 
the tangential pressure which at the end of the palzozoic era 
crumpled the crust and raised the Appalachian arches acted 
then for the first time. The grand catastrophe which shaped 
our Eastern States and closed the palzozoic era in North Amer- 
ica may have been not its first, but its final, manifestation, and 
may have been preceded by others of equal, or even of greater, 
intensity. It is by no means unlikely that the same force that 
raised the Allegheny Mountain arches also raised, in Mid-Silu- 
rian days, a similar arch of the hard, semi-crystalline rocks like 
those of the South Mountains, from whose wreckage the ™* 
dina Sandstone was made. As it rose it was torn down by ai i 
waves, its quartz dispersed, and a new rock formed at a lowèf 
evel. 
A time of rest ensued. The deposition of quartz ceased and 
the Upper Silurian rocks were formed., But the resting e 
came to an end and the earth-force again manifested itself i 
crumplings set in and a new ridge was elevated, which "a 
call the Oriskany Ridge, as from its material the Oriskany pared 
stone was probably formed. This, though thin when gaer i 
with the massive Medina, covers an equal or a pee 
country, and in material the two can scarcely be one f 
Rest again ensued, and the formation and depo sa sa 
and pebbles again ceased. The huge beds of the ee 
. Middle Devonian were formed, and meanwhile the pen p 
accumulating for another thrust. is 
At last it came. The long pent-up force son 
ance. Another time of disturbance set in. Ano pie: 
Archzan area was brought within the deanna 
overcame the #° 
th 
