1815.) An Essay on Rents. ; 215 
the bended position to the strata of this part: while these strata 
close to the rent have contracted, as usual, less on the under side 
p ethan on the upper side / J. Hence also the distance between 
the straight strata on opposite sides of this rent is equal to that be- 
tween similar parts of the bent strata. 
An example of the second mode is that which follows. Some- 
times the strata near bended-tabular rents are all, or nearly all, 
straight, notwithstanding they are situated at different levels on 
opposite sides. ‘Thus the strata ABC, fig. 2, and those which lie 
between them, are straight on both sides of the rents D E; but the 
parts of the strata ) fk and e 2» are higher on the under sides than 
the parts cg 7 and d hm on the upper sides of these rents. The 
strata in this figure, as well as those near all rents of this shape, are 
thicker on the upper than on the under sides; and by this greater 
thickness the stratum A is higher at le than at ¢ d, the stratum B 
at fi than at g h, and the stratum C at k than atl m. Now, as 
has been befure shown, this difference in the thickness of the strata 
is a consequence of the unequal contraction of the stratified matter ; 
that is to say, the strata have contracted more near the upper sides 
than near the under sides of these rents. But although they have 
contracted with different ratios on different sides, yet in the example 
before us the ratio on any one side has been uniformly the same 
throughout the strata, instead of being, as in general, the least 
near the rents, and the greatest at given distances from them. In 
consequence, then, of this uniformity in the ratio of contraction 
of the strata, 2hen taken on one side only, they are straight on both 
sides of some rents, although they are situated at different levels on 
opposite sides of such rents. 
It may be proper to remark here that, though the strata are 
straight, and higher on one side of a rent than on the other, when 
seen in a cross section, as in fig. 2; yet when a view is taken at 
right angles to this section, or when a person faces the rent, every 
stratum then separates at one horizontal extremity into two parts, 
one inclining very gently upwards, and the.other downwards, till] 
opposite the middle of the rent; then the higher part dips down- 
wards, and the lower part rises upwards, till they meet again at the 
other horizontal extremity of the rent. 
2. Observations on the Upper Extremities of large Bended-Tabular 
; Rents. 
_ The > i extremities of some rents are altogether situated in 
solid rock, and at considerable distances below the surface. 
ny large rents extend downwards from the surface of the solid’ 
rock, or that of the solid strata, to great depths ; but some of them 
reach above the solid, through the alluvial matter, to within a few 
inches of the earth’s surface. 
Some of the rents which reach nearly to the surface are precisely 
of the same dimensions in the alluvial clay, as in the solid rock 
’ 
