LATERAL COMPRESSION. 
109 
the arrangement of rocks composing the earth’s crust differs 
materially from that which would result from a mere series 
of vertical movements. Had the volcanic forces been con¬ 
fined to such movements, and had the stratified rocks been 
first formed beneath the sea and then raised above it, with¬ 
out any lateral compression, the geologist would never have 
obtained an insight into the monuments of various ages, 
some of extremely remote antiquity. 
What we have said in Chapter V. of dip and strike, of the 
folding and inversion of strata, of anticlinal and synclinal 
flexures, and in Chapter VI. of denudation at different peri¬ 
ods, whether subaerial or submarine, must be understood be¬ 
fore the student can comprehend what may at first seem to 
him an anomaly, but which it is his business particularly to 
understand. I allude to the small height above the level of 
the sea attained by strata often many miles in thickness, 
and about the chronological succession of which, in one and 
the same region, there is no doubt whatever. Had stratified 
rocks in general remained horizontal, the waves of the sea 
would have been enabled during oscillations of level to plane 
ofi’ entirely the uppermost beds as they rose or sank during 
the emergence or submergence of the' land. But the occur¬ 
rence of a series of formations of widely different ages, ail 
remaining horizontal and in conformable stratification, is ex¬ 
ceptional, and for this reason the total annihilation of the 
uppermost strata has rarely taken place. We owe, indeed, 
to the sideway movements of lateral compression those an¬ 
ticlinal and synclinal curves of the beds already described 
(Fig. 55, p. 74), which, together with denudation, subaerial 
and submarine, enable us to investigate the structure of the 
earth’s crust many miles below those points which the miner 
can reach. I have already shown in Fig. 56, p. 76, how, at 
St. Abb’s Head, a series of strata of indefinite thickness may 
become vertical, and then denuded, so that the edges of the 
beds alone shall be exposed to view, the altitude of the up- 
heaved ridges being reduced to a moderate height above 
the sea-level; and it may be observed that although the in¬ 
cumbent strata of Old Red Sandstone are in that place near¬ 
ly horizontal, yet these same newer beds will in other places 
be found so folded as to present vertical strata, the edges of 
which are abruptly cut ofi*, as in 2, 3, 4 on the right-hand 
side of the diagram. Fig. 55, p. 74. 
Why the Height of the successive Strata in a given Ee- 
gion is so disproportionate to their Thickness. —We can not 
too distinctly bear in mind how dependent we are on the 
joint action of the volcanic and aqueous forces, the one in 
