360 Mr Milne on the Parallel Boads of Lochaber, 



when I find Mr Darwin adverting to traces of shelves at Kilfinnin, 

 and in the valley of the Spey, in support of his theory. 



But if Mr Darwin^'s views are sound, traces of shelves should not 

 be confined to the two localities just mentioned ; they should be 

 visible in other parts of the country of equal height as the Lochaber 

 mountains. 



On the other hand, if it should appear that there are in many 

 valleys, distinct beach lines, all horizontal, and presenting no uni- 

 formity of height above the sea, the argument against a sea theory 

 will be strengthened, whilst a strong analogy will arise to favour the 

 lake theory, — if these beach lines, precisely similar in all essential 

 features to those of l^ochaber, can, from their inland situation, and 

 other circumstances, be clearly shewn to have been produced by the 

 waters of lakes. 



I proceed therefore to mention a few localities out of many, where 

 phenomena similar to those of Glen R,oy are observable. 



(1.) At Inverournan (about 40 miles SW. of Lochaber) there is 

 a lake called Loch Tulla, about 3 miles in length, and 1 in breadth. 

 A stream enters from its east and west ends. Its surplus waters are 

 discharged from its south side, by the river Urchay. 



Two years ago, I discovered all round this lake indications of three 

 levels at which its waters had stood, the lowest being about 183^ 

 feet, the second 277 feet, and the highest 474 feet, above their pre- 

 sent level.* Loch Tulla I roughly estimated at 540 feet above the 

 sea. This lake, therefore, extending originally to about 6 miles in 

 length and half a mile in breadth, had sunk 197 feet, — at which 

 level it had stood long enough to form the second shelf; it next sunk 

 93^- feet, — when the third shelf was formed ; after which it sunk 

 183^- feet — viz., to the present level of the lake. 



It is unnecessary for me to enter into the proofs, that what I am 

 now describing are really beach lines. Their perfect horizontality, 

 which I ascertained by a spirit-level, looking at them from 12 or 15 

 different places along the banks of the lake, — their general confor- 

 mity in sweeping round headlands, and retiring into valleys or burn- 

 courses, — and the extent of flat surface at the levels of the different 

 shelves, afford convincing and irrefragable proofs. 



The difficulty here, as in other similar cases, is to discover, what 

 could have dammed up the lake so much above its present level. 

 The blockage, whatever it was, must have existed somewhere in the 

 valley through which the river Urchay flows. The country, on all 

 other sides of Loch Tulla, rises much higher than 500 feet above its 

 present level. The two lowest shelves are traceable for some distance 

 down the valley of the Urchay, — the middle shelf for about half a 

 mile, and the lowest considerably farther. My notion is, that this 

 valley had been formerly filled with a great accumulation of gravel 



* These measurements were made by a mountain barometer, checked by the 

 sympiesometer. 



