370 
SPENCER : ON THE GEOLOGY OF CALDERDALE. 
dry land and probably connected with the great Brito-Scandinavian 
continent. Two or more great rivers came down from this ancient 
continent loaded with sediment, and emptied themselves into this 
sea in which the Carboniferous Limestone was being deposited. In 
Derbyshire this limestone is about 5,000 feet in thickness, but as we 
trace it northwards it gradually becomes thinner, until in Northum- 
berland and Central Scotland thick beds of shale, sandstone, and 
coal are interbedded in the limestone ; showing that clear water 
prevailed in the south whilst the northern areas were invaded by 
mud-bearing cm rents, and minor elevations permitted the formation 
of land surfaces. These alterations of land and water conditions 
continued throughout the time during which the Mountain Limestone 
of Derbyshire was being deposited. At length the great rivers from 
the north-west and north-east extended their deltas down to Central 
England, covering up the Mountain Limestone with the Yoredale 
strata and Millstone grits. The Rough Rock, the uppermost bed of 
the Millstone Grit Series, near Halifax, consists of two members, an 
upper thick-bedded coarsely-grained, and false-bedded rock, from 70 
to 100 feet in thickness. At the base of this series, in the neigh- 
bourhood of Halifax, there are eight to ten feet of fine-grained flag- 
stone, which sometimes lies under the grit without any parting of 
shale, and at others has an intervening bed of shale of varying thick- 
ness. This lower flag-rock occurs at Moor End and Oxenhope 
Quarries without any covering of Rough Rock, where it is described 
by the Geological Surveyors as the Second Grit Rock." 
The structure of Ringby Hill affo~ds a good example of the 
strata composing the Millstone Grit and Coal Measures. Ringby 
Hill forms a portion of the semi-circle of high-ground, forming the 
outcrop of the Lower Coal Measures, which extends from Swill Hill 
(1,300) and Ringby Hill (1,100) on the north,, to Beacon Hill (850) 
on the east, and which stands up boldly from 500 to 600 feet above 
the Rough Rock upon which the town of Halifax stands. Overlying 
the Rough Rock at the base of the hill is a bed of seat earth upon 
which reposes a thin bed of coal, overlaid by 40 to 50 feet of shales. 
* The Author has endeavoured to show (Trans. Man. Geol. Soc, vol. xiii., 
p. 107) that this flagstone is a necessary part of the Rough Rock, and after 
re-examining the exposures sees no reason to alter this opinion. 
