182 A MEMOIR OP ROBERT ETHERIDGE, F.R.S. 
Later on he read before the Cotteswold Naturalists’ 
Club an interesting paper “ On the Physical Structure of 
the Northern Part of the Bristol Coal Basin, chiefly having 
Reference to the Iron Ores of the Tortworth Area.” Deal- 
ing historically with the subject, he pointed out that the 
“ process of smelting was carried on prior to the use of 
coal, and that wood was used as fuel for the reduction or 
conversion of the raw' ore to the metallic state ” — perhaps 
from the time of the Roman occupation until nearly the 
middle of the eighteenth century. 
After the researches of Dr. Wright and of Charles Moore 
on the Rhaetic Beds (zone of Avicula contorta) in this 
country, it w^as thought desirable by the Director-General 
of the Geological Survey to ascertain how far the strata 
could be represented on the Geological Survey maps. 
H. W. Bristow and R. Etheridge were accordingly instructed 
to “investigate the matter, and they examined and mea- 
sured the sections at Saltford, Uphill, Aust, Garden 
Cliff, Watchet, Penarth, and other places.^ The lower 
portion of the Rhaetic formation was then taken to consist 
“ of alternations of hard and soft marls, passing gradually 
into the red and green marls of the Keuper formation ” ; 
the central portion included the Aust Bone-bed and the 
black shales with Avicula contorta ; while the upper portion 
comprised the Cotham marble or Landscape stone and 
various white limestones and marls, in mass grouped as 
the White Lias. Etheridge thus became keenly interested 
in the Rhaetic formation, and described in detail the beds 
at Garden Cliff near Westbury-on-Severn, at Aust Cliff, 
Penarth and Lavernock, and also those at Watchet. 
Interest in these strata, which connect the New Red 
Sandstone series with the Jurassic system, has been 
generally maintained, and especially in the country around 
Bristol, where the strata have been so well exposed in many 
See Geol. Mag., vol. i. 1864, p. 236. 
