304 
SPENCER : THE HALIFAX COAL STRATA. 
The outcrop of these beds forms a very striking feature in 
the physiography of our neighbourhood, ranging from Swill Hill 
(1,300 ft.) on the north, round by Ringby Hill (1,100 ft.), Beacon 
Hill (850 ft.), and Sowthowram on the east ; standing from 500 ft. 
to 600 ft. above the Millstone Grit Rock at their base, they form 
a bold escarpment facing the west. 
The great estuary in which these rocks were deposited was 
covered towards the close of the Millstone Grit period with a wide 
extent of sand-banks wdiich rose above the level of the waters, but 
were intersected by numerous water-channels. Then subsidence of 
the area took place and the sand-banks were levelled and the 
channels filled up, thus producing that well-known feature of false- 
bedding so characteristic of the Rough Rock. Then the whole area 
was covered with a deposit of clayey mud (seat-earth) and upraised 
into a land surface, ^vhich subsequently became covered Avith the 
greenery which ultimately was converted into the thin coal now 
found overlying the Rough Rock. This is the lowest seam of coal 
in the Yorkshire coal-field. We have seen this coal exposed in 
many places in this district. It varies from 4 in. to 8 in. in 
thickness, but near Elland, where it was formerly worked, it was 
2 ft. 4 in. in thickness."^ 
The whole area again sank beneath the sea-level, and to the 
south of this district the sea invaded the area, and has left evidences 
of its sojourn in a bed of marine shells — Goniatites, Aviculo- 
pectens, etc., but these fossils have not been recorded from the 
Halifax district at this horizon. From 40 ft. to 50 ft. of shales 
overlie this Sand Rock Coal followed by 20 ft. of the Low Bed 
Stone = Soft Bed Flags, of the Huddersfield district. Then a bed of 
seat-earth was deposited and a land surface was again formed, upon 
which was produced the vegetation which formed the Soft Bed Coal. 
Once more the land sunk beneath the waters of an estuary in 
which myriads of freshwater mussels (Anthracosia) and Spirorbis 
flourished, which have left their remains in beds of from 4 ft. to 
12 ft. in thickness. Two species of these shells, viz., A. rohusta and 
>S'. carbonarius have a world-wide distribution, and occur more or 
* Geology of Dewsbury, Huddersfield, and Halifax, p. 5. 
