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591 
among sedimentary rocks, and which are commonly attributed to 
the agency of forces acting from below rather than to pressure from 
without. 
The embankment is fifty-four feet in height, and rests on vegetable 
soil, beneath which are four feet of alluvial clay; then occurs a bed 
of gravel varying from ten to three feet in thickness, but which thins 
out in some places, and under it is the regular London clay, traversed 
in almost every direction by slimy joints. The surface of the coun- 
try gradually slopes towards the Brent, the difference of level between 
the south side of the embankment and the Brent being about twenty 
feet. 
On the night of the 21st of May 1837 the embankment began to 
settle, and in the morning it was found that the foundation had given 
way, and that on the south side, or towards the Brent, a mass of 
ground, fifty feet long and fifteen feet wide, had protruded from under 
the earthwork. During the four succeeding months this mass con- 
tinued to increase in dimensions, and the disturbance to extend, so 
that the surface, for a considerable distance from the base of the 
embankment, had assumed an undulated outline, and the subjacent 
beds, where cut into, exhibited corresponding curvatures, overlappings 
and cracks, the whole of which are described in the memoir, but can- 
not be rendered intelligible without diagrams. In the embankment 
itself the symptoms of failure were confined to a settlement of about 
fifteen feet, and a large fissure near the top, on the side opposite to 
that where the foundation had vielded, and which extended the whole 
length of the slip. To this fissure, and its dip towards the disturb- 
ance at the base of the embankment, the author particularly directs 
attention, as he infers from it the nature and inclination of a fault 
exhibited in the diagrams which illustrate the memoir. 
At the end of twelve additional months, during which the embank- 
ment continued to slip, and the disturbance at the base to increase, 
Mr. Brunel directed a supplementary earthwork or terrace to be 
thrown down upon the swollen surface, and it was an effectual re- 
medy. Up to this time the total subsidence had exceeded thirty 
feet ; and the swollen ground, which extended nearly 400 feet in 
length, and from seventy to eighty feet in width, had attained an 
average height of ten feet, with a horizontal motion of fifteen feet ; 
but the general disturbance ranged to a distance of 220 feet from 
the foot of the slope, or to the Brent, the bank of which was forced 
five feet forwards : the faults varied from thirty feet to two feet, and 
th contortions had attained a curvature, the semi-axis of which was 
irt many places eight feet. 
‘The author then dwells on the magnitude of the disturbance, and 
on the effects which may have been produced in the strata com- 
posing the earth’s surface, by pressure from above. He says, that in 
consequence of the great inequality in the thickness of the sedimen- 
tary rocks, due to the conditions under which they were deposited, 
great inequality of pressure must have arisen, and consequently con- 
tortions and faults have been produced, varying in amount according 
to the thickness and the degree of consolidation in the strata them- 
selyes. In support of his argument, the author quotes a passage 
