144 Geological Society. 
PROCEEDINGS OF LEARNED SOCIETIES. 
GEOLOGICAL SOCIETY. 
November 17th, 1920.—Mr. R. D. Oldham, F.R.S., 
President, in the Chair. 
The following communication was read :— 
‘Eeology of Plants from the Westphalian and the Lower Part 
of the Staffordian Series of Clydach Vale and Gilfach Goch 
(East Glamorgan).’ By David Davies, F.G.S. 
A generic record has been made of 45,000 plants taken from ten 
horizons of the Westphalian and the lower part of the Staffordian 
Series of Clydach Vale and Gilfach Goch. The ten horizons 
are in ascending order: Five-Foot, Middle Yard, Upper Yard, 
Nine-Foot, Red, Six-Foot, Four-Foot, Two-Foot-Nine, Pentre, 
and Abergorky. 
It is found that, for any one horizon, the generic proportion 
yemains constant, even though examination of shales was made 
4000 yards apart; but, when the horizons are taken vertically, 
there is often a complete alteration in the balance. 
Equisetales are found to be the dominant forms on four of the 
ten horizons, Filicaleson three, Pteridosperms on three, Lycopodiales 
on two, Cordaitales on one. A notable fact is that, when Lyco- 
podialés are dominant, the Filicales and Pteridosperms are rare, 
and vice versa. 
It is believed that physical changes occurred in the past, causing 
the altered balance of the plants throughout the ten horizons, 
and that, whereas low lands and swampy conditions favoured 
Lycopodiales, elevated land probably favoured the Filicales and 
Pteridosperms. 
It seems that a cycle of more or less elevated land prevailed 
from the Five-Foot Seam times to the Six-Foot Seam times, followed 
by a cycle of depression, which extended from the Two-Foot-Nine 
Seam times to the Pentre-Seam times, and that a further cycle of 
ye-elevation of land-surface prevailed from the Abergorky-Seam 
times to the No. 2 Rhondda-Seam times. 
At the base of the Staffordian Series a lithological change 
occurs, accompanied by the incoming of smooth rounded pebbles of 
coal, and by an influx of new species; this suggests the probable 
presence of a geological and paleontological break at this horizon. 
