Dr. C. Ricketts—Oscillation of the Karth’s Crust. B09 
dissolution of the snow which, during the Glacial period, enveloped 
the British Isles, Northern Europe, and North America. The re- 
elevation of the land to a certain height was ascribed to the removal 
of the pressure by the melting of this load of ice and snow; but in 
consequence of the accumulation of Boulder-clay which remained, 
it was not raised to so great an extent as before the submergence. 
The present gradual rise of the land in Norway and Spitzbergen may 
also be attributed to the partial removal of once greatly augmented 
snow-fields. 
The immense amount of material removed, and the depth and 
width of valleys formed, indicate, not only the erosion to which 
strata have been subjected, but likewise that there has been a rising 
of the land to expose it to the action of subaerial agencies. If the 
land sinks as a consequence of the deposition of strata, there will be 
little difficulty in attributing upheaval to the effects of denudation, 
when the many thousands of feet of strata which have been removed 
are taken into consideration. The enormous amount of denudation 
to which Paleozoic strata in South and North Wales have been sub- 
jected was made apparent in the well-known sections by (Sir) A. C. 
Ramsay, in which the mass of material displaced has been illustrated 
by contour lines,! and may be recognized as having taken place to a 
greater or less extent in all the older rocks. 
Captain C. E. Dutton states that “those areas in the Colorado 
district which have been uplifted most have been most denuded ; 
he thinks we ought to turn the statement round and say that those 
regions which have suffered the greatest amount of denudation have 
been elevated the most; thereby assuming the removal of the strata 
as the cause and the uplifting as the effect.” * 
An examination of hilly districts demonstrates that Captain Dut- 
ton’s remarks have a general application in different areas in our 
own country. Where denudation has been greatest, elevation prevails 
to the greatest extent, and the oldest deposits not unfrequently form 
the highest ground; or hills, sculptured during a previous geological 
era, and subsequently depressed beneath accumulated strata, have 
again risen as these deposits have been removed, and the former 
crest stands conspicuous as the summit of a mountain. 
In North Derbyshire, near Buxton, the highest portion of the 
Carboniferous Limestone, forming the “ water parting” between the 
east and west of England, is 1500 feet above the sea-level, and is 
surmounted in the neighbourhood by ridges only, composed of 
Millstone Grit, some of which run up to 1800 or even to 2000 feet.’ 
The whole thickness of later Carboniferous strata,—the Yoredales, 
Millstone Grit and Coal-measures, amounting to more than 5000 feet, 
—has been removed by denudation; but on every side such strata dip 
away from the dome-shaped mass to lesser elevations. 
In the district of Craven in Yorkshire the Carboniferous Limestone 
1 Memoirs of the Geological Survey, vol. i. plates 4 and 5, vol. ili. plate 28. 
Referred to by Fisher, op. cet. p. 222. 
2 The Geological History of the Colorado River, Nature, vol. xix. 1879, p. 251. 
> Memoirs of the Geological Survey, North Derbyshire, p. 2. 
DECADE II.—VOL. X.—NO. VIII. 23 
