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56 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 23, 
We have here indeed an “‘upcast fault,’ as stated in the above 
paper, but the present cutting shows us that the strata have not only 
been elevated towards the chalk escarpment, but have been subjected 
also to a considerable subsidence and a partial bouleversement. These 
perhaps are just theseffects which might be supposed to result from 
the geological conformation of the Weymouth district. 
On examining the surface-map of Sir H. De la Beche and the 
Dean of Westminster, we find that the axis of the forest marble is 
very considerably nearer Ridgway than Portland, and therefore that 
the elevating power acted more directly on the northern part of the 
arc than on the southern. But the chalk escarpment would at first 
offer considerable resistance to an upward movement, until the hard 
bed of the Oxford oolite was at length fractured and snapped off. 
Then it was progressively elevated, with all its supermeumbent strata 
grinding and producing the vertical wall of chalk. 
The same elevating power having less resistance further south, 
protruded the forest marble between Chickerel and Langton Herrimg, 
and this effect led to a corresponding removal of a large mass of 
matter on both sides of the anticlinal axis, but particularly on the 
shorter side of the arc, 2. e. on the Ridgway side. 
This removal of matter from the sides to the centre of the are 
would be necessarily connected with a proportionate depression of its 
extreme points, and their maximum depression would be simultaneous 
with the maximum elevation of the central boss. 
This joint action of elevation and depression would, I apprehend, 
involve the upper Purbeck and Hastings sands in all the cireum- 
stances in which we find them placed,—I mean, both tilted up and 
overthrown. 
The subterranean results of this supposed state of things would be 
the fracture of the Oxford oolitic stratum and great pressure on the 
subjacent Oxford clay,—a pressure however exceedingly concentrated 
at the base of the chalk range, as is evidenced by the verticality of 
the strata. Now this local pressure would, it seems to me, foree up 
the Oxford clay from beneath through the opening thus made, that 
is, through the very place in which we find it—between the chalk 
wall and the overturned upper surface of the Hastings sands. 
I cannot but feel that the geology of this part of the Weymouth 
district is connected with some difficulties, and my attempt has 
merely been to suggest a mode of reconciling with the acknowledged 
truths of geological science what, primd facie, appeared somewhat 
anomalous. ‘The impressions therefore which I received from per- 
sonal examination, modified or confirmed by much subsequent con- 
sideration, I beg to offer with entire deference to those better que 
to form a correct judgement on the subject*. 
* Since my examination of the locality and my announcement of its results to 
Professor Sedgwick, I find that Captain Ibbetson has been on the spot; I hope 
therefore that more light will be thrown on the question. 
