lxxxii PEOCEEDINGS OF THE GEOLOGICAL S0CIE1T. [May 1906, 



denudation, with the consequence that the Upper Palaeozoic rocks 

 rest upon the upturned and eroded edges of the older rocks, over- 

 lapping them to rest on rocks of all ages — from Arenig to Upper 

 Ludlow. The amount of material removed from the centre of the 

 arch at this period must have been over 20,000, nay, perhaps over 

 30,000 feet. 



That the surface was for some time uneven is probably indicated 

 by the sudden expansion of the Old-Red-Sandstone rocks in the 

 neighbourhood of Ullswater, which (as has been suggested by many 

 writers) were probably deposited in an old valley. 1 But, as the 

 result of continuous erosion and the filling-in of the deeper 

 depressions by the Old Red Conglomerate, a comparatively-level 

 surface was produced, which is still marked along the Pennine 

 Chain east of Appleby, and especially in the Ingleborough district, 

 where it has not been affected by the later movement that 

 produced the Lake-District dome. The former general evenness of 

 the surface in the Lake District itself is indicated by the very 

 gradual changes in the level of the old basement-plane between 

 Carboniferous and older rocks, changes which coincide with those in 

 the inclination of the Carboniferous strata themselves. 



(c) The Formation of the Carboniferous Rocks. 



As bearing upon the question of the former extension of Carboni- 

 ferous rocks over the site of the Lake District, the existence of 

 a group of rocks on the eastern side of the district of earlier age 

 than the basement-rocks found in the Ingleborough area is of 

 interest. The Shap Limestone there occurs below the Knipe-Scar 

 Limestone, which (with some higher beds) is referred by the officers 

 of the Geological Survey to the Melmerby-Scar Limestone, in turn 



1 I speak of these rocks as Old Red Sandstone, the geological group 

 to which they were assigned by the earlier writers on the district. It has 

 recently become the fashion to term them basement Carboniferous. In 

 the absence of fossils the exact date cannot be determined, but the rapid 

 changes in their thickness, and especially the occurrence of another uncon- 

 formity above them, marked by the existence of a conglomerate-rock with 

 quartz-pebbles, whereas the conglomerates of the Old Red are polygenetic 

 (composed of pebbles of Silurian grits, and more rarely limestones and volcanic 

 rocks and Skiddaw Slate), suggest that some time elapsed between the formation 

 of these rocks and the true basal Carboniferous deposits. Their lithological 

 characters are certainly suggestive of Old Red Sandstone, and physically the 

 base of the old Carboniferous plane is connected with the quartz-pebble- 

 bearing conglomerate and not with that of the polygenetic conglomerate. 



