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Antiquity of Man,' one would suppose that there were at most three terraces. So that one must imagine the valley to have been emptied of water or hollowed out of the land at three swoops-at a hop, a step, and a jump. Whereas the name of the terraces is legion. Looking from the inn door at Roy-bridge on your right is a very broad terrace on which stands the farm of Achderrig. Follow the road towards Bohinnie along the side of this terrace, you will find it cut into several minor terraces, each with its corresponding terrace on the other side of the valley. As you walk up Glen Roy you are always accompanied by from five to ten terraces ever beginning, ever-ceasing. They are in every stage of existence and of vanishment. In some places it may happen that on one side of the valley the terrace is only faintly delineated, or perhaps obliterated, while on the opposite side there is a large patch of alluvial plain still left. That no writer should have mentioned the multiplicity of these terraces, is to me wholly unaccountable. For it is the open sesame' of the secret of the formation of the terraces, besides showing the extreme gradualness of the erosion and formation of the valley. If any one wishes to see the causes which formed our valleys still hard at their work, let him visit Glen Roy and Glen Spean. I do not doubt that terraced alluvial

Lake of Auvergne first

patches are very general affairs, and that indications of them, more or less clear, will be found in all river valleys which have rapids or gorges.'

Any one may make 'parallel terraces,' for himself in the road-side gutter. Dam the run of rain; a pool will form above the dam. Every rain will deposit on the bed of the pool, till the flat alluvium

Take away the

6

rises to the height of the dam.
dam. The run of rain cuts through the alluvium
which it has deposited, and runs between two
parallel terraces till they vanish by denudation.
This is the whole secret of the terraces of Glen
Roy or of any other valley or river. Neither ice-
dam,' nor glacial epoch,' nor sea-shore, nor lake
is required. Dr. Adams found such deposits at
the second cataracts of the Nile, 130 feet above
its present bed. The principle of the formation of
the bluffs of the Mississippi, the loess of the Rhine
and Danube, the terraces of the Somme, &c., may
be exactly shown in the wayside puddle.

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But from the above and from what follows, one would think that Lyell supposes denudation of hills only to go on in the neighbourhood of sheets of water and lakes, that is, wherever a lake or fiord exists;' and that, when the sheets of water have vanished, or the lakes have been filled up, the denudation ceases. For he describes (' Elements,"

filled with al- chapter xvi.) the filling up of the enormous ancient

lakes of Auvergne by the denudation and deposit from the wash of rain. But he neglects to infer that the same denudation must still go on there, and deposit from that denudation somewhere; and that this denudation of land and deposit in water must pervade the entire terraqueous globe.

6

Page 362, he writes: Before entering on any details, I may observe, that the study of this region, and of the others above alluded to, possesses a peculiar interest, very distinct in kind from that derivable from the investigation either of the Parisian or English tertiary strata.'

(One cause of 'peculiar interest' is, that the deposits have been inland; that is, by comparison, on land, and therefore contain the fossils of the animals which inhabited the land.)

For we are presented in Auvergne with the evidence of a series of events of astonishing magnitude and grandeur, by which the original form and features of the country have been greatly changed, yet never so far obliterated but that they may still, in part at least, be restored in imagination. Great lakes have disappeared; lofty mountains have been formed by the reiterated emission of lava, preceded and followed by showers of sand and scoriæ; deep valleys have been subsequently furrowed out through masses of lacustrine and volcanic origin. At a still later date, new

C

luvium, then

cut into hills

and valleys by

rain and rivers.

cones have been thrown up in these valleys; new lakes have been formed by the damming up of rivers, and more than one creation of quadrupeds, birds, and plants have followed in succession; yet the region has preserved from first to last its geographical identity; and we can still recall to our thoughts its external condition and physical structure before these wonderful vicissitudes began, or while a part only of the whole had been completed. There was first a period when the spacious lakes, of which we still may trace the boundaries, lay at the foot of mountains of moderate elevation, unbroken by the bold peaks and precipices of Mont d'Or, and unadorned by the picturesque outline of the Puy de Dôme, or of the volcanic cones and craters now covering the granitic platform. During this earlier scene of repose, deltas were slowly formed; beds of marl and sand several hundred feet thick deposited; siliceous and calcareous rocks precipitated from the waters of mineral springs; shells and insects imbedded, together with the remains of the crocodile and tortoise, the eggs and bones of waterbirds, and the skeletons of quadrupeds, some of them belonging to the same genera as those entombed in the gypsum of Paris. To this tranquil condition of the surface succeeded the era of volcanic eruptions, when the lakes were