366 
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 cases 
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 
haye 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 Boulennais, 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 eleyation 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 
haye been produced by one simultaneous and momentary effort of 
the elevatory force. It is not, however, to be regarded as a neces- 
sary consequence of this conclusion, that the whole elevation of the 
district was thus produced at once; it might be in some degree pro- 
duced by previous, and in a considerable degree by subsequent 
movements; but it would seem at least highly probable, that that 
general movement which produced the dislocations of the elevated 
mass, and impressed upon it its present distinctive characters, should 
have been the most energetic of those repeated movements to which 
the whole elevation has probably been due. 
