VAST THICKNESSES OE STRATA. 
Ill 
A like phenomenon is exhibited in every mountainous 
country, as, for example, in the European Alps ; but we need 
not go farther than the north of England for its illustration. 
Thus in Lancashire and central England the thickness of the 
Carboniferous formation, including the Millstone Grit and 
Yoredale beds, is computed to be more than 18,000 feet; to 
this we may add the Mountain Limestone, at least 2000 feet 
in thickness, and the overlying Permian and Triassic forma¬ 
tions, 3000 or 4000 feet thick. How then does it happen 
that the loftiest hills of Yorkshire and Lancashire, instead 
of being 24,000 feet high, never rise above 3000 feet ? For 
here, as before pointed out in the Alleghanies, all the great 
thicknesses are sometimes found in close approximation and 
in a region only a few miles in diameter. It is true that 
these same sets of strata do not preserve their full force 
when followed for indefinite distances. Thus the 18,000 feet 
of Carboniferous grits aiid shales in Lancashire, before al¬ 
luded to, gradually thin out, as Mr. Hull has shown, as they 
extend southward, by attenuation or original deficiency of 
sediment, and not in consequence of subsequent denudation, 
so that when we have followed them for about 100 miles 
into Leicestershire, they have dwindled away to a thickness 
of only 3000 feet. In the same region the Carboniferous 
limestone attains so unusual a thickness—namely, more than 
4000 feet—as^to appear to compensate in some measure for 
the deficiency of contemporaneous sedimentary rock.* 
It is admitted that when two formations are unconforma- 
ble their fossil remains almost always differ considerably. 
The break in the continuity of the organic forms seems con¬ 
nected with a great lapse of time, and the same interval has 
allowed extensive disturbance of the strata, and removal of 
parts of them by denudation, to take place. The more we 
extend our investigations the more numerous do the proofs 
of these breaks become, and they extend to the most ancient 
rocks yet discovered. The oldest examples yet brought to 
light in the British Isles are on the borders of Rosshire and 
Sutherlandshire, and have been well described by Sir Roder¬ 
ick Murchison, by whom their chronological relations Avere 
admirably worked out, and proved to be very different from 
those which previous observers had imagined them to be. I 
had an opportunity in the autumn of 1869 of verifying the 
splendid section given in Fig. 82 by climbing in a few hours 
from the banks of Loch Assynt to the summit of the moun¬ 
tain called Queenaig, 2673 feet high. 
The formations 1, 2, 3, the Laurentian, Cambrian, and Si- 
* Hull, Quart. Geol. Joum., vol. xxiv., p. 322. 1868. 
