and there, as they died away, they left their terminal and lateral moraines still as well defined in some cases as moraines in lands where glaciers now exist. Frequently, too, masses of stone, that floated on the surface of the ice, were left perched upon the rounded 7'oches moutonnks^ in a manner somewhat puzzling to those who are not geologists. " In short, they were let down upon the surface of these rocks so quietly and so softly, that there they will lie, until an earthquake shakes them down,. or until the wasting of the rock on which they rest precipitates them to a lower level."

It was the opinion of Agassiz, after visiting Scotland, that the Grampians had been covered by a vast thickness of ice, whence erratic blocks had been dispersed in all directions as from a centre; other geologists after a time adopted the opinion — Mr. Robert Chambers going so far as to maintain, in 1848, that Scotland had been at one time moulded by ice. Mr. T. F. Jamieson followed in the same track, adducing many new facts to prove that the Grampians once sent down glaciers in all directions towards the sea. "The glacial grooves," he says, " radiate outward from the central heights towards all points of the compass, although they do not strictly conform to the actual shape and contour of the minor valleys and ridges." But the most interesting part of Mr. Jamieson's investigations is undoubtedly the ingenious manner in which he has worked out Agassiz' assertion that Glenroy, whose remarkable " Parallel Roads " have puzzled so many investigators, was once the basin of afrozen lake.

Glenroy is one of the many romantic glens of Lochaber, at the head of the Spey, near to the Great Glen, or the valley of the Caledonian Canal, which stretches obliquely across the country in a northwesterly direction from Loch Linnhe to Loch Ness, leaving Loch Arkaig, Loch Aich, Glen Garry, and many a highland loch besides, on the left, and Glen Spean, in which Loch Treig, nmning due north and south, has its mouth, on the south. Glenroy opens into it from the north, while Glen Gluoy opens into the Great Glen opposite Loch Arkaig. Mr. Jamieson commenced his investigations at the mouth of Loch Arkaig, which is about a mile from the lake itself. Here he found the gneiss ground down as if by ice coming from the east. On the hill, north of the lake, the gneiss, though much worn and weathered, still exhibited well-marked striae, directed up and down the valley. Other markings showed that the Glen Arkaig glacier not only blocked up Glen Gluoy, but the mouth of Glen Spean, which lies two miles or so north of it on the opposite side.

At Brackletter, on the south side of Glen Spean, near its junction with Glen Lochy, glacial scores pointing more nearly due west, but slightly inclining to the north, were observed, as if caused by the pressure of ice from Glen Lui. The south side of Glen Spean, from its mouth to Loch Treig, is bounded by lofty hills — an extension of Ben Nevis, the highest of these peaks exceeding 3,000 feet. Numerous

gullies intersect their' flanks, and the largest of these. Cony N'Eoin, presents a series of rocky amphitheatres,, or rather large caldrons, whose walls have been ground down by long-continued glacial action: the quartz-veins are all shorn down to the level of the gneiss, and streaked with fine scratches, pointing do^vn the hollows and far up the rocks on either side. During all these operations the great valley was probably filled up with ice, which would close Glen Gluoy and Glen Spean, and might also close the lowest of the lines in Glenroy. But how about the middle and upper Hues?

A glacier crossing from Loch Treig, and protruding across Glen Spean, would cut off Glens Glaibu and Makoul, when the water in Glenroy could only escape over the Col into Strathspey, when the first level would be marked.

Now let the Glen Treig glacier shrink a little, so^ as to let out water to the level of the second line by the outline at Makoul, and the theory is complete. When the first and greatest glacier gave way, Glenroy would be nearly in its present state.

The glacier, on issuing from the gorge at the end of Loch Treig, would dilate immensely, the right flank spreading over a rough expanse of syenite, the neighbouring hills being mica-schists, with veins of porphyry. Now the syenite breaks into large cuboidal blocks of immense size. These have been swept before the advancing glacier along with other debris, and deposited in a semicircle of mounds having a sweep of several miles, forming circular bands which mark the edges of the glacier as it shrunk from time to time under the influence of a milder climate.

This moraine, which was all that was wanting to ( f mplete the theory laid down by Agassiz, is found on the pony-road leading from the mouth of Loch Treig towards Badenoch. A mile or so brings the traveller to the summit-level of the road, and beyond the hill a low moor stretches away to the bottom of the plain. Here, slanting across the slope of the hill towards Loch Treig, two lines of moraine stretch across the road. At first they consist of mica-schists and bits of porphyry, but blocks of syenite soon become intermingled. Outside these are older hillocks, rising in some places sixty and seventy feet high, forming narrow steep-sided mounds, with blocks fourteen

feet in length sticking out of the surface, mixed with fragments " of ^^ !\

mica-schist and gneiss. The inner moraine consists, almost wholly, of large blocks of syenite, five, ten, fifteen, and five-and-twenty feet long.

The present aspect of Glenroy is that of an upper and lower glen opening up from the larger Glen Spean. The head-waters of Lochaber

GLACIAL PERIOD. 45/

gather in a wild mountain tract, near the source of the Spey. The upper glen is an oval valley, four miles long, by about one broad, bounded on each side by high mountains, which throw off two streams dividing the mica-schist from the gneissic systems; the former predominating on the west side, and the latter on the east. The united streams flow to the south-west for two miles, when the valley contracts to a rocky gorge which separates the upper from the lower glen. Passing from the upper to the lower glen, a line is observed to pass from near the junction of the two streams, on a level with a flat rock at the gorge, and also with the uppermost of the three lines of terraces in the lower glen. This line girdles the sides of the hills right and left, with a seemingly higher sweep, and is followed bytwo other perfectly parallel and continuous lines till Glenroy expands into Glen Spean, which crosses its mouth and enters the great glen a little south of Loch Lochy. At the point, however, where Glenroy enters Glen Spean, the two upper terraces cease, while the lower of the three appears on the north and south side of Glen Spean, as far as the pass of Glen Muckal, and southward a little way up the Gubban river and round the head of Loch Treig.

In Scotland, and in Northern England and Wales, there is distinct evidence that the Glacial Epoch commenced with an era of continental ice, the land being but slightly lower than at present, and possibly at the same level, during which period the Scottish hills received their rounded outlines, and scratched and smoothed rock-surfaces; and the plains and valleys became filled with the stiff clay, with angular

scratched stones, known as the "Till,"' which deposit is believed byMessrs. Geikie, Jamieson, and Croll to be a 7noraine profo7idej the product of a vast ice-sheet.

In Wales, Professor Ramsay has described the whole of the valleys of the Snowdonian range as filled with enormous glaciers, the level of the surface of the ice filling the Pass of Llanberis, rising 500 feet above the present watershed at Gorphwysfa. In the Lake District of Cumberland and W^estmorland, Mr. De Ranee has shown that a vast series of glaciers, or small ice-sheets, filled all the valleys, radiating out in all directions from the larger mountains, which formed centres of dispersion, the ice actually pushing over many of the lesser watersheds, and scooping out the great rock-basins in which lie the lakes Windermere, Ullswater, Thirlmere, Coniston W^ater, and Wastwater, the bottoms of which are nearly all below the sea-level. The whole of this district, he has showTi, experienced a second glaciation, after the period of great submergence, in which valley-glaciers scooped out the marine drift, and left their moraines

in the Liza, Langdale, and other valleys, and high up 'in the hills, as at Harrison's Stickle, where a tarn has been formed by a little 7?iorai7ie, acting as a dam, as shown by Professor Hull.

In Wales, also, valley-glaciers existed after the submergence beneath the Glacial sea. Thus in Cwm-llafar, under the brow of Cameddi Dafydd, and Carnedd Llewelyn, Professor Ramsay has shov/n that a narrow glacier, about two miles in length, has ploughed out a long narrow hollow in the drift (which "forms a succession of terraces, the result of marine denudation, during pauses in the re-elevation of its submersion) to a depth of more than than 2,000 feet."*

The proofs of this great submergence, succeeding the era of "land-ice," are constantly accumulating. Since 1863, when Professor Hull first divided the thick glacial deposits of Eastern Lancashire and Cheshire into an Upper Boulder Clay, and Lower Boulder Clay divided by a Middle Sand and Gravel, the whole of which are of marine origin, these subdivisions have been found to hold good, by himself and Mr. A. H. Green, over 600 square miles of country around Manchester, Bolton, and Congleton; by Mr. De Ranee over another 600 square miles, around Liverpool, Preston, Blackpool, Blackburn, and Lancaster, and also in the low country lying between the Cumberland and Welsh mountains and the sea.

In Ireland, also, the same triplex arrangement appears to exist. Professors Harkness and Hull have identified the " Limestone and Manure Gravels '' of the central plain, as referable to the " Middle Sand and Gravel," and the " Lower Boulder Clay" rests on a glaciated rock-surface along the coasts of Antrim and Down, and is overlain by sand, which, in 1832, was discovered by Dr. Scouler to be shell-bearing. At Kingstown the three deposits are seen resting on a moutonneed surface of granite, scored from the N.N.W.

In Lancashire and on the coast of North Wales, between Llandudno and Rhyl, Mr. De Ranee has shown that these deposits often lie upon the denuded and eroded surface of another clay, of older date, which he believes to be the product of land-ice, the remnant of the moraine prof ojide, and the equivalent of the Scotch "Till." He also shows that. the Lower Boulder Clay never rises above an elevation of fifty or eighty feet above the sea-level; and that the Middle Sand and Shingle rests directly upon the rock, or on the surface of this old Till.

Near Manchester the Lower Boulder Clay occasionally rests upon an old bed of sand and gravel. It is extremely local, but its presence has been recorded in several sections by Mr. Edward Binney, who

• Professor Ramsay, "The Old Glaciers of North Wales." Longman, 1S60.

was the.first to show, in 1842,'^ that the Lancashire Boulder Clays were formed in the sea, and that the erratic pebbles and boulders, mainly derived from the Cumberland Lake Districts, were brought south by means of floating ice.

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