BY HUGH MILLEK. 295 



on the summit of our Island it must have been slicing by the sea ; 

 and I now return to our proper question — How the present fea- 

 tures have been impressed on the outcrops of the strata. "Why do 

 the hard beds rise into scarped ridges, and the softer ones retire 

 into furrows ? 



Theories of Escarpment-Formation. — Geology has comparatively 

 lately passed through what I may call her mythologic stage; 

 growing away from which it was inevitable that the true should 

 be accepted only after the false had been tried and found want- 

 ing. Hence it is that the answers to this question elsewhere 

 have been at once various, and, in many cases, crude. It will 

 serve as an historical resume and otherwise elucidate the subject 

 if we take up the several theories one by one, and try their vir- 

 tue upon these IN'orthumberland escarpments. The first clearly 

 belongs to the mythological stage. 



1 . Old Diluvial Theory. — The Scottish capital is picturesquely 

 broken and overlooked by grand masses of rock, long familiar as 

 *' the phenomenon of Crag-and-Tail." These were once the centre 

 of such attention as escarpments received. '' All its steeper pre- 

 cipices present their iron fronts to the west, while towards the east 

 its slopes are prolonged and gentle. The Castle and Calton rocks, 

 the erect front of Salisbury Crags, the western flanks and dark 

 brow of Arthur Seat, the trap precipices that rise over Lochend, 

 the low trap precipices of Hawk Hill, all look to the west, as if 

 watching the advance from that quarter of an enemy who had 

 wasted them of old."* The general opinion upon the Crag-and- 

 Tail at the end of last century was that the deluge, sweeping 

 eastwards, had torn away the softer rocks from around these 

 more durable masses, leaving them rent and craggy in front. 

 Long afterwards Sir James Hall, in an elaborate paper in support 

 of this view, pointed to the Crag-and-Tail, as well as to wide- 

 spread debris of Western origin, and to scores and scratches on 

 the rooks, in proof of some such tumultuous diluvial wave.f 



* Crag-and-Tftil is now-a-ilays a term restricted to tlio glacial phenomenon of a boss 

 of roclc with glacial deposits preserved on its lee-sido; which some of these arc. Others — 

 notably Salisbury Crags, are Escarpments. 



t Trans. Royal Soc, Edinburgh, Vol. VII. 



