THE GROWTH OF CONTINENTS. 
129 
as it is called, above them at its base, — this term, 
unconformable, signifying merely that the two 
sets of strata are placed at an entirely different 
angle, and must therefore belong to two distinct 
sets of deposits. But there are two series of 
geological facts connected with this result which 
are often confounded, though they arise from 
very different causes. One is that described 
above, in which, a certain series of beds having 
been raised out of their natural horizontal posi- 
tion, another series has been deposited upon 
them, thus resting unconformably above. The 
other is where, one set of beds having been de- 
posited over any given region, at a later time, in 
consequence of a recession of the sea-sliore, for 
instance, or of some other gradual disturbance 
of the surface, the next set of beds accumulated 
above them cover a somewhat different area, and 
are therefore not conformable with the first, 
though parallel with them. This difference, 
however slight, is sufficient to show that some 
shifting of the ground on which they were accu- 
mulated must have taken place between the two 
series of deposits. 
This distinction must not be confounded with 
that made by Elie de Beaumont : we owe it to 
D’Orbigny, who first pointed out the importance 
of distinguishing the dislocations produced by 
gradual movements of the earth from those 
