118 
EFFECTS OF 
of the strata, depend on the mode of application of the force, the 
jointed structure of the rocks, and their condition of load or pressure. 
According as the impulse and resistance are uniform, or determined 
to particular directions, the effects must vary, accordingly, and from 
these we may infer the former. 
The Ribblesdale system indicates linear impulse, in a north-east and 
south-west direction, the Penine system a general impulse determined 
to various lines, by the jointed structure and unequal weighting of 
the rocks : the Greenhow system, placed at the intersection of the 
Ribblesdale and Penine displacements, has the character of impulse 
at a point, or interrupted line. 
Thus far successful let us next inquire into the cause of the remarka- 
ble and almost constant relation of displacing and displaced planes. This 
is not a local but a general fact, liable to exceptions in particular districts, 
but of great theoretical importance. It appears a natural consequence of 
the dynamical conditions of the problem. (See Diag. No. 19.; Any 
extended mass of horizontal strata, a b c, yielding to a mechanical 
force normal to the surface must break at right angles d d, (i e ver 
tically) or at unequal angles, x x. If the former case there is no 
reason 4 priori why one part should be lifted or depressed more 
than another, (many vertical veins are thus circumstanced and have 
no tlnow.) If the latter, and one side be relatively elevated, as A 
or B, the part bxx being unsupported can not be raised from A at 
all, if the rock be much jointed, or at all events without some of 
its parts being unsupported and falling so as to produce fissures and 
and veins more or less inclined in confusion toward x x ; A on the 
contrary may be lifted and the beds of B retain their order and regu- 
larity, the lateral pressure being transferred horizontally to close up 
the parallel joints near the throw. 
It follows that displacing planes which intersect strata at other 
than right angles, and are not accompanied by great confusion on 
the hanger (upper) side, must in general dip under the depressed por- 
