6G6 
PROFESSOR PRESTWICH OR THE ORIGIN 
are alike. The advocates of the “ marine theory ” point to the worn and rounded 
detrital materials, to the beds of sand and the boulders before alluded to, and to 
the numerous local gravel terraces throughout Scotland as evidence of marine agency, 
but their number, their limited range and differences of level, point to- the operation 
of independent local causes rather than to an uniform general cause such as a sea level. 
The phenomena admits also of explanation by land waters and other causes to be men¬ 
tioned hereafter. Professor Nicol’s* answer relative to the coincidence of the “ road” 
levels with those of successive cols, which he explains by checked tidal currents, 
cannot be considered satisfactory. The improbability, amounting almost to impos¬ 
sibility, of a series of such coincidences as a period of rest concurring with the level 
of each col during the general emergence of the land must be apparent. 
Further, the fact that nowhere have marine organisms been found in the drift 
ascribed to marine origin, has been urged as an argument against the marine hypo¬ 
thesis. It is true that, in loose sand and gravel, shells may have been dissolved out 
by the percolation of water; but considering the extent of the debris, the many 
sections, and the occasional presence of argillaceous seams, it is difficult to understand 
their absence everywhere. It must, nevertheless, be borne in mind that even in those 
low levels, which there is every reason to suppose have been submerged, marine 
remains are very rare (postea, p. 691). f 
Mr. Milne Home does, however, in a later paper, refer to two finds of shells,— 
one on the top of Unachan Hill, and the other in a field near Spean Bridge. But the 
specimens were not seen by him. In both instances they were found near the surface, 
and directly under the peat, and from the way in which his informant speaks of them, 
I should judge that they were recent shells by chance buried there. 
§ 2. The Glacial Theory of Agassiz : Mr. Jamieson’s Exposition. 
Agassiz and Buckland, who visited Scotland together in 1840, came to the 
conclusion that with respect to the “parallel roads” of Lochaber “the glacial theory 
alone satisfied all the exigencies of the phenomena, ”§ Agassiz suggested that a 
glacier, “issuing from the valley of Loch Arkaig, crossing Loch Lochy, and damming 
up Glen Gluoy below Low Bridge,” would explain the origin of the lake and highest 
“ road” in Glen Gluoy. A second great glacier descending from Ben Nevis, crossing 
* Qaart. Journ. Geol. Soc., vol. xxviii., p. 237, 1872. 
t Sir T. Dice-Lauder, speaking of the long and deep cuttings of the Caledonian Canal, says that 
“ after cutting through a thick stratum of moss, nothing hut sand, clay, gravel, and rounded stones 
were found .... nor has the slightest appearance of marine exuviae been anywhere discovered.”— 
Op. cit., p. 27. Darwin, however, states that he was informed that broken sea-shells were found in the 
lower part of the gravel at the head of Loch Ness, at a point about 40 to 50 feet above the level of the 
sea.—Phil. Trans, for 1839, p. 57. 
£ Trans. Roy. Soc. Edinb., vol. xxviii., p. 116, 1877. 
§ “The Glacial Theory and its recent Progress.” By Louis Agassiz. —Edin. New Phil. Joum., 
vol. xxxiii., p. 236, 1842, 
