Geology at the British Association. 387 
numerous, which include many fossiliferous horizons, yielding 
a rich flora, several rare crustacea, some fragmentary fish 
remains, and numerous freshwater lamellibranchs. An 
abundant marine fauna has also been obtained from several 
horizons. The thickest marine bed has been mapped, and, 
using it as an index bed, the position of the pot, pipe, and 
fireclays in the Moira sandstones can be fixed. This marine 
bed is comparable with the Gin Mine marine bed of the North 
Staffordshire coalfield, with the Mansfield marine bed of the 
Yorkshire and Nottinghamshire coalfield, and with the 
Pennystone ironstone marine bed of Coalbrookdale. 
Mr. G. Barrow gave further views on the Systems of Folding 
in the Paleozoic and newer rocks. From evidence on the 
flanks of crystalline areas in the Highlands, Ireland, Anglesea, 
and the Isle of Man, it was seen that the margin was a great 
line of resistance, and the folding in the adjacent Paleozoic 
or newer rocks was parallel to it, and was the cause of the 
strike of the folding. Under earth-stresses the softer rocks 
have buckled up against a great resisting crystalline mass. 
There was, therefore, no Caledonian movement, but only a 
series of resisting masses with parallel margins. The writer 
believed that in South Britain and North France the tracing 
of the outer margins of crystallization will prove that the 
Hercynian System simply means that the boundaries of the 
resisting crystalline masses against which the newer rocks 
buckle up now trend east and west. This will explain the 
local departure of the strike of the folding in the North of 
England; the lines of resistance locally depart from their 
usual trend and the subsequent folding does the same. 
Dr. Gertrude L. Elles described the relation of the Rhiwlas 
and Bala Limestones at Bala. The difficulties in the inter- 
pretation of the Bala district were largely due to the imper- 
sistent nature of the limestones and their inconstancy as to 
horizon. The Rhiwlas limestone is an impersistent limestone 
at the base of the Hirnant series, and is found only in the 
northern part of the area. The Bala limestone is not developed 
as a calcareous bed in the northern part of the area, but is 
somewhat more persistent as a definite band in the southern 
and eastern portions of the district. The true relation is 
seen in the type section at Gelli Grin, where the Bala limestone 
at its maximum thickness is overlain by light-coloured pasty 
mudstones containing a typical Rhiwlas limestone fauna. 
Miss Elles also read a paper on the shelly and graptolitic 
faunas of the British Ordovician, in which she described the 
two main types of ‘shelly’ faunas of Ordovician Age, (a) 
Asaphid-Trinucleid-Calymenid fauna, and (+) Cheirurid-Lichad- 
Encrinurid fauna. She showed that they could be further 
divided into a number of sub-faunas which can be correlated 
1913 Novi. 
