SIMPSON : STRATA AND DEPOSITION OF THE MILLSTONE GRITS. 417 
-whole marine tract, and the deposition of the Yoredale rocks began." 
Thus we are brought up to the Millstone Grit period, when it is 
evident important changes took place. We speak of the Carboniferous 
period as one when sub-aqueous areas were almost constantly, though 
intermittently sinking, the downward movement about keeping pace 
with the deposition of mechanical sediment. But simple depression 
does not explain the phenomena of the Grits ; we require something 
more, positive oscillations of level, alternating elevations and depres- 
sions, and it is highly probable that movements of both kinds occurred 
just prior to and during the deposition of the Grits. 
In the first place, we have this unequal bottom on which the 
Kinderscout is laid, and the fact that the district in which the Grits 
are thickest, that is, in Derbyshire, Lancashire, and the south of 
Yorkshire, is also that in which the Yoredales attain their maximum 
development. This unequal bottom is shown by the overlap against 
what were doubtless elevated Yoredale areas, of the higher members 
of the Kinderscout ; the lower beds were deposited in the hollows, 
and abut unconformably against elevated Yoredale beds, and it was 
not until further subsidence occurred, submerging these elevations, 
that the higher Kinderscout beds were laid over the whole area. 
Then we must also consider the great change in the nature of the 
Grit deposits from those of the preceding series. 
The Kinderscout, especially, is exceedingly coarse, and succeeds, 
generally, beds of shale and much finer sandstone. It is also very 
persistent, and does not shade away as might be expected into finer 
grained sandstone, away from the source of supply, so that in addition 
to the unequal subsidence of sub-aqueous areas, we are almost forced 
to assume that there was considerable upheaval of the land over 
areas from which the supply of material was derived. Jukes-Browne, 
discussing this, says : — *" I see only one way in which such a change 
could be brought about, and that is by a general and considerable 
elevation of the area, raising the central parts of the island into those 
atmospheric regions where rain, frost, and wind are most vigorous and 
incessant in their action " ; and he adduces actual evidence in favour 
of this from Flintshire, where, near Mold, the Grit is of small and 
* Building of the British Isles, Jukes-Browne, p. 140. 
