Hugh Miller — Escarpments and Terraces. 25 



mentation, — and when, moreover, it is found in the best preservation 

 on the water-shed of the country, — marine and fluvial theories must 

 clearly be set aside. Two theories remain. The first — supported, 

 and for certain districts established, by Eamsay, Greenwood, Foster, 

 and Topley, and others — attributes the etching out of these features 

 to the protracted influence of atmospheric disintegration ; the other — 

 enunciated by Mr. Goodchild — calls in for the Yorkshire terraces, and, 

 as I trust I have shown, necessarily also for the Northumberland 

 escarpments, the force of glaciers eroding unequally along beds of 

 unequal resistance. 



West Northumberland offers a fair field for testing the latter theory. 

 Where the ice- sheet can be proved to have passed athwart the escarp- 

 ments, and full against their scarped faces, it could not have been the 

 cause originating them. However, the striated and moutonneed rock 

 surfaces, transport of boulders, etc., agree in recording that the ice 

 moved from the west in a direction sufficiently near the E.N.E. strike 

 of the ridges to favour Mr. Goodchild's theory in a high degree. In 

 at least later glacial times a certain obliquity of flow tended against 

 the scarped slopes, but as rock-markings tell of but the later and last 

 glaciation, an allowance must be made and the coincidence assumed 

 as complete. The harder lines of bedding must, therefore, have 

 withstood erosion, and the softer yielded to it, and assuming a plane 

 surface to begin with, the result might somewhat have resembled the 

 present featuring; though whether so much sharpness of outline 

 could have been attained is more than questionable. 



In proceeding further it will be necessary to summarize Mr. Good- 

 child's evidence, (1) negativing the atmospheric disintegration theory 

 as applicable to the terraced outcrops of the Yorkshire limestones, 

 and (2) supporting his theory of their origin by glacial erosion. To 

 this will be added (3) a statement of collateral difficulties raised. 



1. Negativing the Atmospheric Theory. — Except near the outburst of 

 springs there is but little disintegrated rock scattered about the 

 limestone outcrops. The dip-slopes, instead of showing excessive 

 signs of weathering on their front portions first uncovered and there- 

 fore longest exposed, seem equally weathered over the whole surface. 

 The swallow-holes also that pit the inner margin of the slope are 

 circular cavities, not trenches lengthened in the direction of dip- 

 slope ; they have therefore originated where they are. Glacial 

 scratches occur within a few feet of the present outcrop of shales 

 and limestones, thus putting a close limit to the amount of denuda- 

 tion accomplished post-glacially. The extreme slowness of at- 

 mospheric disintegration is proved by a comparison of the gradual 

 recession of a waterfall with that of the steep sides of the gorge it 

 leaves. In one extreme case the former receded 40 feet to the 1^ ft. 

 of each side. 



2. Supporting the Glacial Theory. — The development of the strata 

 of sandstone, limestone, and shale, is not in the ratio of their durability 

 under atmospheric disintegration, but as their resistance to mechani- 

 cally grinding force. Under the former agent limestone ranks lowest, 

 owing to its comparatively great solubility in acidulated water; 



