324 Geological Society. Mr. Hopkins on the Wealden District. 



This force is not supposed to have been necessarily of uniform in- 

 tensity throughout. If it has been greater in one portion of the 

 district than in the rest of it, a corresponding modification will be 

 produced in the directions of the lines of elevation, or a deviation 

 from those positions in which they would have existed had the in- 

 tensity of the force been uniform throughout. If the force has been 

 uniform, the directions of the lines of dislocation and elevation will 

 depend on the form of the boundary of the surface of the elevated 

 area. If this be given, these directions must be investigated on me- 

 chanical principles ; and if the force be supposed to have acted with 

 greater intensity in any assigned portion of the district, the corre- 

 sponding modification in the directions of the lines must be deter- 

 mined. This has been done by the author in some particular caseo 

 in the memoir above referred to in the Transactions of the Philoso- 

 phical Society of Cambridge. 



Any irregularity in the cohesive power of the elevated mass will 

 have but little effect on the general directions of the lines of eleva- 

 tion ; but if there be any considerable continuous portion of the di- 

 strict throughout which the elevated crust is thinner, and therefore 

 lighter and weaker, the effect will manifestly be the same as if the 

 crust had been of uniform thickness throughout, and had been acted 

 on in this particular portion with a force of greater intensity. Con- 

 sequently the modifications in the lines of elevation will be the same, 

 whether they arise from a weaker crust or a greater intensity of force. 



In the application of this theory, the boundary of the area under 

 which the elevatory force has simultaneously acted must be de- 

 termined as nearly as may be by the actual boundary of the dis- 

 turbed district, throughout which we recognize a character of con- 

 tinuity in the phenomena of elevation. That portion of the district 

 also in which the force may appear to have acted with greater in- 

 tensity must be determined by the existing indications of greater 

 elevation. Thus it is conceived, that a simultaneous effort of the 

 elevatory force was made throughout the whole tract extending from 

 the Bas Boulonnais on the east, beyond the Wiltshire Chalk on the 

 west, and from the Vale of Pewsey and the valley of the Thames on 

 the north, beyond the southern coast of this country on the south. 

 The Wealden district, with the Bas Boulonnais, presents us also 

 with a case, in which it is presumed, from its greater elevation, 

 either that the disturbing force acted there with greater intensity, 

 or that the elevated crust was there thinner, than in the other part 

 generally of the district. Assuming such to have been the case, the 

 author points out what would be the general directions of the lines 

 of elevation throughout the Wealden and the Bas Boulonnais, and 

 comparing them with the lines described in the first part of his pa- 

 per, he shows the remarkable accordance which exists between the 

 results of observation and of theory ; an accordance which he considers 

 as strongly confirmatory of his theory as applied to this district. 



Hence the author concludes, that the fissures or dislocations in 

 which he conceives all the observed lines of elevations (whether 

 faults, anticlinal lines, or lines of flexure,) to have originated, must 



