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Darwin's Agenda for Lochaber

This document (University Library, Cambridge, Darwin MS 50, 'Glen Roy notes and scraps') is a single sheet of paper, watermarked 1837. The sides are numbered, in ink, 13 and 14, and the page appears to have been retained from a series on which Darwin had made notes on MacCulloch's and Lauder's papers before visiting Lochaber (the final sentence of these notes appears at the top of the sheet). My own notes in explanation of each agendum are appended.

 

Chief Points to be Attended to

The shelves according to MacCulloch must be due to accumulation, to Dick [Lauder] to corroding.—where cut off (Dick) truncated below level. —but MacCulloch disputes this truncation.

1.^st Nature of shelves, with respect to foundation

2. Organic remains. Balani. Serpula. - calcareous matter

3. Abrupt termination of shelves. - cause - examine hill of Bohuntin - where terminates, is rock corroded as would be from tides. -

4.^th Is there lip of escape to shelf. 3.^rd Glen Fintac

5.^th Are there 2 [nd] and 3 [rd] shelves in Glen G[l]uoy.

6.^th Relative height of 2^nd shelf and Loch Spey

7.^th Does Alluvium vary above upper shelf

8.^th Has it much lubricity.

9.^th Are there traces of more lines than the three

10.^th How far are the furrow[s], now occupied by streams, irreconcileable with the idea of lake or sea

11.^th The relative preservation of the shelves.

12.^th The great problem, why lines absent in other parts. The Hill of Bohuntine and Glen Turrit must answer this. -

13.^th Examine Tom-na-fersit and entrance of Loch Treig for Balani. and smooth waterworn rocks, also Barnacles on transported blocks. -

14.^th Shelves correspond to head of plains

15.^th Form of valleys of Glen Roy and Gluoy, and of Hill of Bohuntine

Notes on Darwin's Agenda (for further explanation, see text of article)

1. i.e., the relation of the Roads to the underlying bedrock, bearing on the question of their formation by erosion of bedrock and/or deposition of débris.

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2. Evidence of marine organisms: barnacles (Balani) and calcareous tube worms (Serpula), being adherent organisms, would give unequivocal evidence of marine conditions in situ, but any fragments of calcareous shelly material would be indicative.

3. Roads R2 and R3 terminate on both sides of the hill of Bohuntine, where Glen Roy and the smaller Glen Collarig open into Glen Spean (Figure 1). On Darwin's hypothesis their termination was due to greater tidal action in the wider valley.

4. Lauder had failed to find any overflow col on the level of Road R2, and Darwin recognized this as a major anomaly. The head of Glen Fintac, which is a small valley tributary to Glen Gluoy, was a plausible point to search for such a col from Glen Roy; in fact the col connecting them is much too high, and the overflow col for R2 was later discovered in a quite different position on the other side of Glen Roy (Glen Glaster).

5. i.e., are the minor Roads reported by MacCulloch in Glen Gluoy (but doubted by Lauder) in fact the fragmentary traces of beaches on the same level as Roads R2 and R3 in Glen Roy ?

6. i.e., does Road Ri in Glen Roy pass over into the head of Glen Spey and survive above Loch Spey (as MacCulloch believed) or is it on the same level as the intervening col R1 (as Lauder maintained)? See also note, above, on agendum 4.

7. On both MacCulloch's and Darwin's interpretations, even the highest Roads (G and R1) represented only transient pauses in a fall of relative water-level from even greater heights, whereas on Lauder's explanation the sequence of temporary lakes had begun at the level of Roads G and R1. Hence the uniformity or otherwise of the superficial débris above and below these Roads might provide a critical test between these alternatives.

8. i.e., could the distinction implied in agendum 7 have been obliterated by soil-creep?

9. i.e., intermediate 'minor' Roads, anticipated at many levels and in many places on Darwin's hypothesis.

10. Origin of minor indentations on the sides of the main valleys, followed by the Roads and only deepened to a minor extent by subsequent erosion by present rivulets.

11. On Darwin's hypothesis, the Roads represented successive pauses in an extremely lengthy process of crustal elevation, so that the lower and more recent Roads might be expected to be better preserved than the higher and older ones.

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12. Darwin's hypothesis required that the localized distribution of the Roads should be attributed to their localized formation and/or preservation, since the sea-level had stood at the same levels on many hillsides on which no Roads were found. The Hill of Bohuntine is at the mouth of Glen Roy (Figure i), and Roads R1 and R2 terminate on its flanks (see also Note to agendum 3). Glen Turrit is a tributary valley near the head of Glen Roy, and has a broad terrace (interpreted by MacCulloch as a delta) on the same level as Road R3.

13. Tom-na-Fersit is a rocky knoll at the mouth of Glen Treig; when the water-13. level was at Road R3/S it would have been a small island, on the shores of which there might be exceptionally clear evidence of marine erosion and/or marine organisms, since it would not have been obscured by any subsequent soil-creep from higher hillsides (see also Note to agendum 2).

14. i.e., Lauder's assertion that at least some Roads are coincident in height with particular cols of flattened form (see also Notes on agenda 4 and 6).

15. The form of these valleys, containing one or more Roads at high levels, might suggest why such Roads occurred there and not elsewhere (see also Notes on agenda 3 and 12).