365 
between these last-mentioned places, the line assumes a distinct an- 
ticlinal character. | 
Transverse valleys exist in the greensand ridge of this part of the 
* district as well as in that on the southern side. The author also 
alludes to what he conceives to be incipient valleys of this descrip- 
tion, and states his reasons for believing them to be indications of 
transverse fractures. He conceives this opinion to be strongly cor- 
roborated by the existence of the perennial springs by which these 
valleys are characterized. Several are pointed out, especially in Leith 
Hill and the Seven Oaks ridge overlooking the valley of the Weald. 
Transverse river-courses through the Chalk escarpment form one of 
the most striking features in the geology of this district. The ana- 
logy which they bear to the transverse valleys across the greensand 
ridges would seem to leave no doubt of their being referrible to the 
same physical cause ;’ and as there are in many instances direct evi- 
dence which renders the origin of these latter valleys in transverse 
fractures highly probable, the same conclusion appears almost equally 
probable with respect to the river-courses through the Chalk. In 
the evidence of dislocation which the Chalk itself affords, there is 
nothing, however, very conclusive; but it must be témistnbered, that 
the evidence of faults is- always difficult to detect in a massive forma- 
tion like the Chalk, possessing not more than two general divisions 
which admit of distinct identification. 
The central chalk ridge of the Isle of Wight is traversed in like 
manner by three transverse valleys, two of which are river-courses. 
The author has pointed out some direct evidence in support of the 
conclusion, that the central one (that of the Medina) has originated 
in transverse dislocation. 
Bas Boulonnais.—With respect to the structure of the Bas Bou- 
lonnais, it is only necessary here to state, that the author has recog- 
nized three parallel lines of dislocation commencing at the coast and 
running in a direction coinciding with that of the lines of elevation 
of the Weald, supposing them produced across the Channel accord- 
ing to the law which they follow on this side of it. The southern- 
most of these lines passes immediately to the north of Boulogne. 
II. In the second part of this paper, previously to his comparing the 
observed phenomena with theoretical deductions, the author recapi- 
tulates some fundamental points of his theory. It is assumed, that 
an elevatory force has acted simultaneously at every poit of the 
lower surface of the elevated mass in each district throughout which 
the phenomena of elevation are observed to follow the same law. 
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 
VOL, III. PART II, 2H 
