228 The American Geologist. April, vnm 
S., Mongr. II, 209). This magnificent exposure of an uncon- 
formity is further referred to as a local illustration of the wicle- 
'jpread erosion of a great mass of land, "afterwards sub- 
merged." As the canyon has an accidental position with re- 
gard to the buried surface, the single section may be taken as 
a fair sample of a much larger area than is actually exposed. 
A buried plain of remarkably even form underlies the 
heavy Carboniferous limestones of northwestern England. It 
has been repeatedly described and figured by English geol- 
ogists. An official report states: — "It is evident that these 
[Carboniferous] beds were deposited on an uneven floor of 
the Silurian rocks, for the line dividing the two formations 
runs sharply up or down 20 or 30 feet in places, while the bed- 
ding of the limestone keeps nearly horizontal. In other 
places .... Silurian grit sticks up in a boss, against the 
west side of which limestone has been laid down in horizontal 
strata" (Mem. Geol. Surv. Gr. Britain, Geol. of the Country 
around Ingleborough, 1890, 23). The inequalities of the floor 
here referred to are very small in comparison to the bights 
that the Silurian strata must have reached after their great 
deformation, for the sections represent the contact surface by 
ari essentially even line, parallel to the limestone beds, and so 
it may be seen on various valley sides; for example in upper 
Ribblesdale. The actual contacts displayed in certain hillside 
quarries on Moughton fell are extraordinarily clear; one of 
them is well reproduced in the frontispiece to Bird's "Geology 
of Yorkshire." 'The heavy Silurian flagstones are so evenly 
truncated that a single layer of limestone stretches smoothly 
over them for a hundred feet or more across the quarry; the 
same limestone blufT may be traced for two or three miles 
around the side of the fell, close above the uppermost out- 
crops of the flagstones; and the same general division of the 
Carboniferous formation lies on the denuded surface over tens 
or scores of miles. As there is no residual soil on the firm 
rocks of the denuded plain, and as the overlying strata are 
heavy marine limestones (excepting local deposits of pebbh 
beds, one or two feet thick), the floor must have been swept 
and worn by the sea before Carboniferous deposition began. 
There seems to be no way of determining how much work was 
thus done by the sea, and how much had been previously done 
