1 68 Notes on the Geological History of - [Sess. 



from the Esk syncline iu the railway cutting east of Niddrie 

 West Junction, shows at once how folded rocks may be planed 

 away, ami how the structure of the country may be masked 

 by the boulder-clay. To link up these broken outcrops with 

 their representatives in the west, one must travel as far as 

 Linlithgow, the rocks of the Edge Coal group, and those above 

 the Edge Coal horizon — the Upper Limestones, the Millstone 

 Grit, and the Coal Measures — having been denuded from the 

 intervening country. It will be observed that the upper 

 edges of the outcrops have been bent to the right, illustrating 

 the drag of the ice-sheet passing eastwards. 



The last episode in this long history, the Ice Age, found 

 the hill a little higher and more rugged than we know it, and 

 separated from the Braid Hills by a gorge deeper, perhaps 

 considerably deeper, than the present valley. The ice-sheet, 

 passing eastwards, swept from its surface the products of 

 decay and moulded its outlines as we see them, leaving striae 

 on its rock surface and a ground moraine of boulder-clay in 

 front and on its lower slopes. 



The glaciated cave (Plate IV.) near Blackford Hill quarry 

 provides an interesting illustration of the vicissitudes of the 

 region in relation to the Ice Age. Undercut in the fault- 

 brecciated andesite by a pre-glacial river, it was scoured and 

 striated by the glacier which passed through the gorge. It was 

 then filled up by glacial (Ubris which choked the valley, a relic 

 of which is the glacial flat which lies between the Braid Hills 

 and the Hermitage. Subsequently re-excavated by streams 

 draining the glacier, streams that cut out the valley at the 

 base of the Corbie's Craig (Plate III.) when the normal 

 channel was blocked, it was again filled up with sand and 

 gravel brought down by these streams. Much of this deposit 

 of sand and gravel remained in place when Agassiz visited the 

 cave in 1840, by which time an exposure about 25 feet 

 in length had been washed out. The remainder was excavated 

 in the early seventies, when the cave was in danger of being 

 quarried away. 



The scene from Blackford Hill before the Ice Age must 

 have presented a remarkable contrast to that which followed. 

 The surface of the country was probably trenched like a 

 stretch of typical ' bad lands ' : a country of scrub-covered 



