16 Bernard Smith — Pre-Triassic StvaUoiv-lioles. 



Pre-Triassic SwaOow-holes in the Haematite District of 

 Furness, Lanes ; a Glimpse of an Ancient Landscape. 



By Bernard Smith, M.A., F.G.S. 



{Published by permission of the Director of the Geological Survey.) 



A POINT of economic imjDortance, as well as scientific interest, 

 ■^ has been brought out by a study of the occurrences of 

 haematite in the Furness district of Lancashire and the neighbou^ring 

 shores of the River Duddon in the Millom district of Cumberland ; 

 namely, that the origin and distribution of the ore-bodies, known 

 as " sops ", is due, in large measure, to the physiographical con- 

 ditions that existed in this area in post-Carboniferous but pre- 

 New Red times. Future explorations for these profitable ore-bodies 

 may be guided by a true aj^preciation of the conditions of formation, 

 which are discussed, in somewhat scattered form, in the recently 

 published Geological Survey Memoir ^ on the " Haematites of West 

 Cumberland, Lancashire, and the Lake District ". 



The following is a more connected resume of the events that 

 gave rise to the soj)S and the reasons for their restricted occurrence. 



We may preface our remarks by stating that (1) the haematite 

 found in the Carboniferous Limestone, both in Cumberland and 

 Furness, is due to a metasomatic alteration of the Limestone, 

 presumably by the descent of iron-bearing solutions stored in the 

 New Red beds that overspread the Carboniferous rocks ; and (2) 

 " sops " may be defined as bodies of ore, circular to oval in form, 

 and narrowing downwards irregularly like deep basins or pockets 

 in limestone. 



It appears that in pre-New Red times the main mass of 

 Carboniferous Limestone formed a widespread plateau extending 

 from near Kirksanton, north-west of Millom in Cumberland, east- 

 ward to near Lindal-in-Furness, and was dominated on the south 

 by a northward-facing escarpment of Yoredale Beds. South-west 

 of Dalton-in-Furness the escarpment looped southward to near 

 Yarlside and Stank, as a sharp V-shaped notch, the eastern wall of 

 which was a pre-New Red fault-scarp trending from north to south. 



At the jDresent day swallow-holes and caverns are abundant on 

 such limestone plateaux, and as fast as the swallows go out of 

 commission, or the cavern-roofs collapse, they become choked with 

 debris, mostly of an angular and open character, and occasionally 

 roofed with turf. So also in this case swallows were formed, and 

 when a hole ceased to serve as an open conduit, material falling 

 from the walls filled the bottom with coarse limestone debris, and 

 included masses of limestone-shales. Disintegrated shale and mud, 

 washed in, formed a rough lining to the whole mass, and in some 

 cases formed a clayey plug at the bottom. The foot of the escarp- 

 ment, also, became the depository of screes or brockrams as 



^ Si5ecial Reports on the Mineral Resources of Great Britain, vol. viii, 1919. 



