San Marcos free press. [volume] (San Marcos, Tex.) 1877-1892, 1878-11-16
GEOLOGICAL CHANGES.
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Prof. Ramsay, describing somc Of the
remarkable faults in North Wales, states
that near Snowtion there is a fault where
the displacement Of the strata amounts
to 5000 feet, and in the Berwyn hills
one of 5000 feet; in the Aran range CO.
ours the Bala fault, with downthrow
Of 1000 feet. Between Ann Mowddwy
and Careg Aderyn the displacement l.
between 10000 and 1900 feet. @Here
we have evidence, Says Mr.. Croll, shat
a mass ofrock, varying from one mile
to two miles in vertical thickness, must
have been denuaed in many places from
the surface of the county in north
Wales" Along the flank OF tho Gram
plans great fault runs from the North
Sea at Stonehavon to the estuary Of the
Clyde, throwing the old rod sandstone
on end sometimes for q distance Of two
miles from the line Of dislocation. Prof.
Geikie concludes that the amount of
displacement must be in some places
not lcss than 5000 feet. But perhaps
the most remarkable instance known Is
that cf the great fault which crosses
Scotland from near Dunbar to the Ayr
shire coast. On the south side of this
fault We find the ancient silurian rocks,
north Of it the less ancient rocks, the old
red sandstone and carboniferous of north
Scotland. The amount of dislocation
is in some places fully $4,000 feet, or
nearly three miles. Now, it is to DO OBJ
served that the dislocation is older than
the carboniferous ora. For originally
the silurian rocks south of the fault must
have been covered by the prolongation
of the old red sandstone, afterward COM
pletely removed by denudation. If the
carboniferous strata had then existed,
they, lying uppermost, would, of course,
have been washed away first. But wc
find them on the south side of the fault,
Lying Immediately on the old silurian
floor, the old red sandstone which origi-
nally covered that floor having been en-
tirely removed. Thus the enormous
thickness of nearly three miles Of old
red sandstone must have been denuded
away during the period which interven-
ed between its deposition and the SUBJ
sequent accumulation of the carbonifer-
GUS limestone and the coal measures
now lying directly on the silurian rocks!
One other case to indicate the enormous
periods required for the formation of
some of the features OF Scottish scenery.
Professor GeilIie has shown that "thc
Pentlands must at one time have been
covered with upward of a mile in thick
ness of carboniferous rocks, which have
all been removed by denudation.'
"Now,' says Mr.. Croll, "the Pcntlands
themselves, it can be proved, existed as
hills in much their present form, before
the carboniferous rocks were laid down
over them; and as they are of lower old
red sandstone age, and have been form
ed by denudation, they must conse-
quently have been carved ont of the old
red sandstone and the beginning Of the
carboniferous age" And, in order fully
to appreciate the vastness Of the periods
required for these and kindred changes,
it is necessary to recognize the extreme
slowncss with which such changes pro-
coed