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W. TOPLET OK AREAS OF APPARENT UPHEAVAL. 189
these rocks would he affected by this amount, besides that resulting
from the thinning of the higher Secondary rocks themselves.
We see, then, that in estimating the dip of the beds in any such
district, our results will vary according to the rocks which are exposed
in it. But inasmuch as our knowledge of the great movements which
have affected the earth's crust is generally deduced from such obser-
vations, this liability to error becomes a very serious matter.
We infer, for instance, because of what we know of the dip
of the Great Oolite in Gloucestershire and Oxfordshire, that the
beds have been upheaved towards the west and north-west, which
has resulted in a dip to the east and south-east, or towards the
London basin. But if, over this area, denudation had gone much
further than it has done, and all the Oolites down to the higher part
of the Lower Lias had been swept away, w r e should observe that the
beds along this line were approximately flat

and we should infer
that there had been no upheaval here, or that the net results of
such movements as had taken place had been to leave the beds in a
horizontal position. If the whole of the Lias had been denuded, we
should infer a slight westerly dip or from the London basin. If
denudation had gone far into the Trias, sweeping away the whole
of the higher Secondary rocks, we might have inferred a considerable
westerly dip

• .

3. The Oolitic RocJcs of Yorkshire. — These afford another very
striking example. It is known that the entire Oolitic series, which
is so magnificently developed in the northern part of the county, is
absent under the Wolds, and that the Bed Chalk there rests directly
on the Lower Lias. In part, no doubt, this is due to the great un-
conformity between the Cretaceous and Oolitic rocks

but it is also
partly due to actual thinning of the strata, the Lower Oolites having
disappeared entirely in this manner.
In order to estimate the amount of the dip which is due to this
thinning, we have only to compare the small actual southerly fall
of the bottom of the Inferior Oolite along the base of the western
escarpment with the great southerly dip which the Coral Crag would
have if it now stretched (as once it did) along the top of that escarp-
ment. But this is not all

for the Lias itself is thinning in the same
manner, and we find that the base of the Lias undergoes comparatively
small changes of level along the same north and south line.
4. The Carboniferous Mocks of Yorkshire. — The Carboniferous
Limestone series of Yorkshire has a general dip, from the high land of

Since this paper was read, Mr. Whitaker has kindly drawn my attention f o
the following remarks by Sir W. V. Guise, in his address to the Cotteswold
Naturalists' Field Club, April 10, 1869. Referring to the meeting of the Club
held on March 25, 18GS, Sir W. Guise says

— " Mr. Lucy mentioned bis having
recently made an excursion in the Cotleswolds round Stow and Burford, and
called attention to the gradual thinning out of the beds in a northerly .?.
direction. On the authority of Mr. Hull's Memoirs, to illustrate Map 44,
Geological Survey, he stated that, while at Cleeve Cloud the Inferior Oolite
attains an elevation of 1130 feet, the Cornbrash south of Burford is not much
more than one half that height. This, however, is in some degree due to the
greatly diminished, thickness of the underlying, strata in the latter locality"
Q.'J. G. B. No. 118.