Bernard Smith — Pre-Triassic Swallow -holes. 17 



the escarpment slowly receded under the action of weathering 

 agents. 



In New Red times both the plateau and escarpment were over- 

 spread by characteristic deposits of dolomitic limestone and breccias 

 (both local), red sands, clays, and shales, relics of which still survive 

 in several places, even where there has been great denudation. 

 In the Newton and Yarlside Mine, in the V-shaped notch above 

 mentioned, the old pre-Triassic fault-escarpment has the irregular 

 outline of a present-day limestone cliff, with the New Red Sandstone 

 still banked against it. 



At some post-Triassic date the area was upheaved, faulted, and 

 subjected to denudation. 



Since the uplift the Yoredale Beds have been worn back by 

 erosion almost 2 miles to their present position near Adgarley and 

 Little Urswick. Farther south they have retreated less. Towards 

 the Duddon shores they are faulted down beneath New Red Sand- 

 stone and do not appear at the surface. 



The upUft further resulted in the downward movement of iron- 

 bearing waters, which attacked the limestone-breccias in the swallows 

 and caverns, or the limestone along faults and joints. 



The mineralizing solutions, entering from above, were concentrated 

 chiefly upon the limestone-breccias, which by nature are peculiarly 

 vulnerable. As the alteration of the limestone fragments progressed 

 the masses of newly formed ore packed together and led to the 

 collapse of the roof and let in the overlying New Red sands and 

 loams in jumbled masses. This episode is recorded in the irregular 

 pockets of such material that are found in the ore of the Park and 

 Roanhead Mines. ^ 



That the above is probably the true story receives confirmation 

 from the following facts : (i) After removal of the ore the limestone 

 walls, in some cases, show a smoothing that is characteristic of the 

 action of water, and presumably was effected before the ore was 

 formed, (ii) The sops are lined with "hunger" and "muck". 

 The former is partly composed of weathered shale like that inter- 

 bedded with the limestone, while the " muck " is probably derived 

 from the ore itself, (iii) Patches of limestone shales are found 

 embedded sporadically in the pure ore. (iv) The ore in the centre 

 of each sop is good soft pick-ore, in small fragments, just such_ as 

 would be formed from a loose breccia that packed together during 

 alteration, (v) Lastly, a mass at least 122 feet iu thickness near 

 its centre, composed of chocolate-coloured clay like a cave earth, and 

 containing many subangular waterworn fragments of limestone, has 

 been found recently, filling the bottom of the Nigel Pit sop at Roan- 

 head, beneath the main mass of ore. It also contains small sandstone 

 fragments and patches of hunger and muck. 



In Furness, therefore, the area in which " sops " may be expected 



1 Summary of Progress for 1916 : Mem. Geol. Surv., 1917, pp. 9-10. 

 VOL.LVII. — NO. I. 2 



