258 PROCEEDINGS COTTESWOLD CLUB 1903 
the forces of the atmosphere, such as rain, frost, and 
carbonic acid, set to work upon it, causing degradation 
and decay; but acting with most effect upon the shales. 
The streams that originated in the area cut their way out- 
wards, wearing away hard and soft strata in their course, 
and carrying out the sediments derived from the wear and 
tear of the rocks. The shales were removed more rapidly 
than the limestones, which stood up as elevations. 
2. THE ORIGIN OF THE DOME 
BY T. MELLARD READE, C.E., F.G.S. 
It is necessary to consider how the dome was produced. 
To take the simplest form in which it could be developed 
we must conceive an injection of fluid or semi-fluid rock 
along a bedding plane, and the raising of the superincum- 
bent strata in a sort of large bubble. This has actually 
occurred in the Henry Mountains—the Black Hills of 
Dacota. In such cases a very little consideration will 
serve to show that the lifted superincumbent strata will be 
subject to tension and fracture. Another mode in which 
a domical anticline can be produced is by compression. 
Imagine a great thickness and extent of horizontal strata 
subject to compression either by internal expansion or 
outside pressure. Mechanical reasoning as well as experi- 
ment show that, when the pressure reaches a critical point, 
the strata will give way by folding in the weakest places. 
These weakest places, I have satisfied myself by experi- 
ment, are determined mainly by the form and inequalities 
of the floor on which the strata have been deposited, hence 
the folding may take a circular, elliptical, or linear form. 
But, whatever form it does take, all sections will have 
more or less curvature. 
