Dr. C. Ricketts—Changes in the Earth’s Crust. 165 
These remind the observer of breislakite, although their presence in 
the felspar-substance instead of lining the vesicles may appear to 
contradict this diagnosis. If they be not breislakite they may possibly 
be cossyrite,’ but their smallness does not permit of a more definite 
determination. 
V.—On some Puysicat CHANGES IN THE Harry’s Crust. 
(Part IIT.) 
By Cartes Ricxerts, M.D., F.G.S. 
: (Concluded from p. 119.) 
(—* the western flanks of the Malverns, the Upper Silurians are 
folded in several great anticlinals and synclinals, formed 
parallel to the axis of the Hill itself. To the west of Ledbury and 
again near Woolhope these contorted strata dip beneath the Old 
Red Sandstone, which, as computed by Phillips, has a maximum 
thickness of 8000 feet,? that of the Upper Silurians being 2690 feet. 
The thickness of the strata of which the Longmynd is formed has 
been estimated by the Government Surveyors at not less than 26,000 
feet, as exposed in their highly inclined edges; the beds dipping at 
an average inclination of 60° to the W.N.W.® They thus appear as 
if they had been tilted by pressure against the more ancient rocks of 
the Caer Caradoc Range. 
In each of these instances the immense accumulations formed may 
have had effect in causing the great disturbance to which the strata 
have been subjected. Whether the ridges of the Malverns or of the 
Caradoc Range are recognized as having once formed the summits of 
ancient mountains, or the dividing ridges between valleys, there is 
abundant evidence that a great thickness of sediment has been 
laid down in their vicinity, burying the slopes on their sculptured 
sides; the deposit being greater at a moderate distance, where the 
slopes extend deeper, than near the summits. 
An example affording more conclusive evidence of the nature of 
the causes by which contortions and cleavage are produced occurs in 
the neighbourhood of Llangollen. At three different periods during 
Paleozoic times, namely, the Lower Silurian, the Upper Silurian, and 
the Carboniferous periods, the area around Llangollen continuously 
sank below the sea-level whilst deposits were accumulating. Three 
times they were raised above that level, and at the same time these 
‘deposits underwent denudation; 7.e. previous to the deposition of 
the Upper Silurians, the Limestone and later Carboniferous rocks, 
and again as we observe at present. During each of these periods 
_ valleys were excavated to a depth so great, that the summits so far 
presented a mountainous character that they were raised 1500 feet 
and more above the then sea-level. 
Previous to the deposition of the Upper Silurian strata, a pre- 
Wenlock valley was excavated in those of the Bala formation to a 
1 H. Forstner, “ Ueber Cossyrit, ein Mineral aus den Liparitlaven von Pantel- 
leria,’”’ Zeits. f. Kryst. 1881, Y 348-362. 
2 Mem. Geol. Survey, vol. i. pt. i. p. 102. 
3 Siluria, 1859, p. 23. 
