1 62 Notes on the Geological History of [Sess. 



might squander hours of reverie, perplexing himself to dis- 

 cover the pylons that guide the birds unerringly to their nests 

 in the bewildering maze of trees. Across the dry valley the 

 Corbie's Craig (Plate III.) is an everlasting challenge to itching 

 feet of aspiring mountaineers. There are said to be secret 

 spots, known to the elect, where, surrounded by a generous 

 flora, aristocratic botanical families have their seat. And in 

 the unsightly quarry recess one may pick up despised frag- 

 ments of precious stones, wonderfully varied in colour and 

 form, fashioned through age-long processes in a laboratory 

 where a million years are as a day. 



Higher on the hill one may indulge historical and poetic 

 fancies, following renowned example. Hither historians come 

 to brighten their perspective, poets to attune their lyre, and 

 artists to study the nuances of light. So we have Scott, 

 ecstatic in the recollection of youthful roving, recalling Scot- 

 land's lost legions to Borough-moor ; Stevenson, no doubt, 

 loitering above the burn whose melody provokes or lulls his 

 song ; and David Koberts lighting up the hills beyond the 

 Campagna with a halo he must have caught on the Moorfoots 

 from Blackford Hill. 



The naturalist, drawn to the hill, it may be, by its botany 

 and its ecology, cannot fail to be arrested by its bold escarp- 

 ments, evidently the stumps of rocks which extended beyond 

 their present limits, its striated surfaces and groove-like 

 depressions, the gorge of the Braid Burn, the dry valley, and 

 the remarkable hollow that sweeps round its north-western 

 front. 



The purpose of these notes is to present some outline of the 

 geological history of the hill implied in the known rock 

 structure of the neighbourhood. 



Admirably exemplifying the familiar crag-and-tail hill form 

 with characteristic curved frontal depression — the ice deflection 

 basin, due to the erosive action of ground ice deflected in its 

 march eastwards by the obstructing crag — a conspicuous wit- 

 ness of the Great Ice Age, seen also at the Castle, Calton Hill, 

 Salisbury Crags, and elsewhere within the boundaries of Edin- 

 burgh, Blackford Hill forms roughly an inclined wedge with 

 its blunt crag apex directed westwards, rising about 300 feet 

 above the ice-deepened hollow, its retreating surface broadening 



