The Scottish Naturalist. 265 



the compass over and over again, sweeping out into the most 

 extravagant curves, now from the right bank, now from the left, 

 till the length of the river's journey is considerably increased. 



Geographically the Earn is situated in a valley running east 

 and west, formed by the Ochill Hills and the lower Grampian 

 spurs of Ben Voirlich on the south, and a tract of variable country 

 ranging from Moncreiffe Hill, through low-lying grounds and 

 lofty eminences, to the culminating height of Ben Chonzie (nearly 

 3000 feet) north of Loch Earn, in the west. Geologically the 

 Ochill Hills are of igneous origin, and consist essentially of 

 "Trap." Moncreiffe Hill on the north is also trap, whence 

 passing westward for several miles, this same material trap breaks 

 here and there through beds of Old Red Sandstone ; thence we 

 pass through Silurian and Cambrian into the gneiss and schistose 

 rocks of the south-western Grampians. The floor of the valley 

 is an alluvial plain, where — 



The spirit of a sea 



Still presiding where it laved 



Tells me that it once hath roll'd. 



It is not, however, the spirit of a sea that haunts this alluvial 

 tract, but the image and superscription of a river, of this river Earn. 



I had noticed, before visiting the lowlands, that when the sun 

 sank at the western end of the valley, and every hillock and 

 undulation became distinctly marked by the opposing shadows, 

 long lines ran here and there across the alluvial tract — now 

 sweeping curve within curve, now with the stream, now forming 

 a greater or less angle to its course ; and in times of flood these 

 self-same lines were seen as well-marked margins to the stranded 

 water. These, along with the alluvial appearance of the valley, 

 is the superscription of the river. The lines and margins are 

 its ancient banks, and show how much it has wandered over 

 the valley in the long lost past. Some of these exhibit com- 

 paratively modern positions of the stream, others relate to 

 changes in a remote antiquity. On descending into the valley 

 to inspect these flood margins, I found that some were channels 

 wide and shallow, others merely represented a difference in the 

 height of the tract by escarpments varying from a few inches to 

 2 or 3 feet. I now saw that there were two distinct levels in 

 the alluvial part of the valley, a higher and a lower "haugh" — 

 the lower averaging 8 feet above the river, the higher reaching 

 26 feet. The flood margins and ancient channels are to be seen 

 only on the lower haugh. 



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