348 Dr. C. Ricketts—Oscillation of the Earth's Crust. 
Gonez, AlbanierCom. (4) Greenstone-trachyte (Richthofen), Unter 
Fernezely, N.E. Nagy Banya, Szathmarer Com. (5) Greenstone 
trachyte, Trapategy, 8.W. Bereghsasz, Beregher Com. I may say 
that in no single instance have I observed the characteristic pleo- 
chroism of the hypersthene in any monoclinic augite. I would therefore 
ask, with Mr. Whitman Cross, whether it is not possible that the 
strongly-pleochroic ‘“angite” extracted by Herr Oebbeke! from an 
andesite from the Sierra de Mariveles, Luxon, may not be hypersthene, 
and whether this pleochroic mineral may not occur in association 
with a non-pleochroic or differently pleochroic augite. 
IIJ.—On AccumuLATION AND DENUDATION, AND THEIR JNFLUENCE IN 
CaAUsING OSCILLATION OF THE Hartu’s Crust. 
By Cuarues RIcKETTS, M.D., F.G.S8. 
(Continued from p. 306.) 
HE Carboniferous Limestone of the north-west of England was 
formed in a bay separated from another marine area farther south 
by a narrow isthmus” and promontory never submerged, extending, 
as Professor Jukes pointed out, in ‘‘a band of country running east 
and west across England from Leicestershire, through Warwickshire, 
South Staffordshire, North Shropshire into Montgomeryshire,” ? and 
to the mountainous district of North Wales. 
The limestone is situated in and fills up valleys formed in Silurian 
and other rocks, and there has evidently been a progressive depres- 
sion during the whole period of its formation; from the time when 
conglomerates and sandstones derived from the neighbourhood were 
distributed over the bottoms of these valleys,‘ forming the so-called 
“Upper Old Red Sandstone” of the Survey Maps, though con- 
sidered by the Members of the Geological staff as forming in such 
cases the base of the Carboniferous series;° and this progressed 
whilst the flanks of these valleys were being gradually submerged, 
the basement beds of the limestone being very frequently composed 
to a great extent of fragments of Silurian rock in a matrix of lime- 
stone. This subsidence continued during the whole period in which 
the strictly marine series, represented by the Carboniferous Lime- 
stone, was being deposited; until and beyond the time when that 
1 Oebbeke, Beitrage zur Petrographie der Philipimen und der Palan-Inseln, Neues 
Jahrbuch, I. Beilage Band, p. 41. 
2 That portion of this isthmus, situated between Coalbrookdale and the Clee Hills, 
was sixteen miles wide at the termination of the deposition of the Carboniferous 
Limestone, and was reduced to twelve miles during that of the Millstone Grit. 
3 Memoirs of the Geological Survey, The South Staffordshire Coal-field; by 
J. Beete Jukes, F.R.S., p. xii. See also Jukes’s Manual of Geology, second 
edition, p. 518. 
* Professor J. Phillips recognized that “they were confined to valleys in the slate 
formation, and never follow that rock to its escarpments on high ground.’’— Geology 
of Yorkshire, part ii., p. 13. 
5 Mem. Geol. Survey, Geology of Kendal, etc., W. T. Aveline, F.G.S., p. 14; 
[Prof.] T. McK. Hughes, F.S.A., p. 15; of Kirkby Lonsdale [Prof.] Hughes, 
p- 16. On the Carboniferous Conglomerates of the Basin of the Eden, by J. G. 
Goodchild, Quart. Journ. Geol. Soc. vol. xxx. p. 396. 
