184 Geological Results of the Earth’s Contraction. 
and a half millions of pounds, or 750 tons ;—also from cohesion 
within the bed, and below. 
The force will travel slowly from A towards X, on account of 
the gravity, cohesion and partial compressibility of the mass: the 
first dislocation will hence take place towards A, and it will there- 
fore produce a bulging, as Bng, A at the same time advancing 
to B. (The distance Ag, for a specific direction of the force, will 
depend on the thickness, gravity and cohesion of the bed. ) 
The force continuing in action, part of it will be transmitted 
towards g and X, owing to the difficult flexibility of the bed ari- 
sing from cohesion and gravity: another part will cause B to ad- 
vance towards C, and tend to raise Bng to Cog. In the same 
manner, C og will tend to change to Dp g. 
But the action upon ¢ is increasing from two sources, viz :— 
1. the propagation of the original force through the bed, which is 
enhanced as the elevation rises ;—2. a new force of vast amount 
proceeding from the gravity of the inclined bed pg. Owing 
to the last mentioned cause, in connection with the yielding 
nature of the material, pg sinks to p’ g, and Dp’ g becomes the 
actual position of the bed instead of Dpg. The sinking of p g, 
d the primal force together, (if the latter were not before sufii- 
cient,) would cause gw to rise to h ww. 
_ The force continuing, the position D p’g is changed succes- 
sively to Ep” h,F p’”i. The greatest propelling power is exerted 
y the gravitation of the inclined bed pg, when its angle of in- 
clination is between 45 and 60 degrees. Beyond 60° the action 
is increasingly downward, and the propelling part of the action 
becomes small. At 90° and beyond, the action is wholly down- 
ward, so that in this position, pg shortens only from the compres- 
sibility of the mass. Now, the action on gw is simply the prim 
force, nearly or quite the whole of which acts upon g X. Thus 
huw rises to ivw; and this again, continuing to rise, changes in 
form in the manner just illustrated. poet 
By this process, therefore, a series of folds would be produced 
each with the inclination steepest on the side farthest from A; 
and moreover, these folds would be necessarily most abrupt the 
nearer they are to A. 
In the above, the lateral force has been supposed to act directly 
upon the borders of an oceanic depression. When the contraction 
in progress produces fractures over the interior of a continent, tl 
continued contraction and increasing lateral pressure, still operat- 
ing upon the same yielding area, might produce plications parallel 
with the line of fracture, which would be most abrupt near it, 
diminish ~ “rs pirinate a fact illustrated in the Urals.* The pli- 
cations wo iffer in extent on the two sides of the line, provided 
the force or the material were different. yt 
* Geology of Russia and the Urals, R. I. Murchison, i, 462. 
