Prof. C. Lapworth—The Secret of the Highiands. 341 
' Tn all the last three cases the final results are almost identical. 
The roof and floor of the overfold (arch-limb and trough-limb) 
repose at once upon each other apparently in regular and conform- 
able succession. 
12. By a series of repeated folds and faults of this nature, a rock 
formation of no great actual thickness lying upon the flanks of an 
ancient mountain range may be made to crop out over an enormous 
area, presenting the fallacious appearance of a massive formation of 
immense thickness, but of a most monotonous petrological character, 
being apparently formed of alternations of similar strata, which 
follow each other in parallel and unbroken order. Or, on the other 
hand, if the strata in this position include those of several distinct 
but conformable geological formations, these same physical accidents 
will necessarily give to the whole mass the fallacious appearance of 
a single and consecutive rock-series, whose strata all agree generally 
in dip, strike, and amount of convolution (Plate VIII. Fg. 8). 
13. As a final result, however, in a theoretically symmetrical 
mountain range, if all disturbing elements are eliminated, broad 
parallel zones of such strata should flank the meuntain range on 
both sides, as we approach the mountain axis. The corresponding 
zones on opposite flanks should be formed of identical strata, and 
answer precisely to each other in amount of convolution and average 
inclination. The crest of the range being longest exposed to denu- 
dation should show an axial zone of the oldest rocks, the youngest 
should occur in the plains at the foot. In other words, the folding, 
the faulting, and the geological age of the strata should all decrease 
in exact proportion as we pass outward from the vertical strata along 
the mountain axis through the plagioclinic rocks of its flanks, to the 
orthoclinic beds of the fringing plains. 
The foregoing are perhaps the main principles which bear upon 
the appearances presented by comparatively homogeneous strata 
looped up by opposed parallel pressures into symmetrical folds of 
infinite length, perpendicular to the plane of curvature. But in 
actual mountain regions, none of these conditions obtain over a large 
area. The rock-formations implicated are very different in litho- 
logical characters, and vary greatly in their relative resistance to 
deformation under pressure. The tangential thrust differs much in 
local intensity, while the major loops are in truth long and irregular 
domes. Hence within a convoluted region all these phenomena must 
vary locally both in form and degree, and may be arrested at any 
stage, or, in the process of time (by the development of new and 
differently applied pressures), may be supposed to be extended 
indefinitely. 
But before treating of the special modifications of the foregoing 
results which take place in nature, there are two additional con- 
clusions which appear to flow so naturally from the application of 
the foregoing principles that they must be noticed in this connection. 
Deformation of Individual Strata. 
14. In all those cases hitherto considered, the masses of strata 
