Below this point, many great terraces become visible on the right hand ; but although they do not correspOnd precisely in level with the third line, as that formerly de scribed does, they do not materially differ in elevation. Many small rivers here enter laterally into the valley in several places ; but it is unnecessary to mention them farther than to remark that, as in other places where no such remarkable phenomena are present, they are accom panied by their own lateral terraces. Still, as we here de scend along the glen, many fragments or traces of lines are seen between the principal ones. These, however, are generally obscure, and have very short courses. In a very few places, it may also be observed, that notwith standing the pertinacious levels maintained by the lines, some slight errors in this respect exist. But when these are examined with care, they will be foand not to affect the general question ; as wherever they occur, they may be traced to the subsidence and derangement of that allu vial surface of the hill on which they were originally im pressed. On the left side, about this place, one large slide may be observed which illustrates this opinion in a very distinct manner—the whole surface having descend ed for a space of many feet. Wherever also such ap pearances of a defective level occur, they will be found to arise from the laws of perspective, as they affect curved surfaces placed above or below the horizontal line.
When the faces of the hills are furrowed by descending torrents, the lines enter these cavities for a certain space; and as this rule is general, with few exceptions, it is un necessary to mark the places where these occur. The fact, however, will hereafter be found of considerable im portance in reasoning on the nature of these phenomena. They are often ploughed across and obliterated by tor rents of recent origin ; sometimes also they terminate ab ruptly in the beds of more ancient ones ; but still the two upper ones may generally be distinctly traced.
From these appearances, we can often determine the re lative difference of age between the hollow or the torrent, and the line ; and we may also ascertain that a part of one cavity is posterior to that mark, and another prior to it. It must also be remarked generally, that the lines are best marked on the straightest sides, or on those slopes which lie in a straight or slightly curved plane, and at somewhat high angles of acclivity ; while they are most obscure where the most numerous sinuosities, torrents, irregularities,. or rocky faces, occur. Among the best marked are the two upper ones on the right hand above Glen Turit, and the three above Glen Fintec on the same side.
About two mi'cs below the head of Lower Glen Roy, a semicircular hollow opens on the right, giving rise to a considerable stream, and falling gradually into Glen Turit. The two upper lines enter a little way into the
hollow, and then disappear : the third or lowest not having yet occurred. On the opposite side of this hollow, or that which adjoins Glen Turit, three lines are to be seen presenting the greatest anomaly visible throughout their course. On a superficial view the two upper ones appear to be a continuation of those formerly mentioned ; but on examining them by the spirit level, it was found that the lowest of these was continuous with the upper one of Glen Roy, and that the highest was a supernumerary one, and that it terminated abruptly at both ends, although of the same general form and appearance as the others. That one which is really continuous with the upper line of Glen'Roy is prolonged into Glen Turit.
A great accumulated mass of terraces, similar to those in the upper part of Glen Roy, is seen at the junction of the two streams which issue from Glen Turit, and from the unnamed hollow just described. This compound mass presents a surface of various heights; but the highest of these corresponds precisely in level with the highest ter races at the top of Glen Roy, and equally so with the lowermost line of the three for which this valley is re markable. This line, indeed, now first comes into view diStinctly ; having for some time been imperfectly visible on the left side, but being here distinctly continuous on the right. The minor terraces which so frequently skirt the river are also visible here, and they accompany it for a considerable space downwards along the bottom of the glen, which still continues to present an irregular alluvial flat.
Independently of these compound and minor terraces which are accumulated below the lowest line, there are also fragments and parts of irregular terraces in various places at a level above it ; besides considerable channelled alluvia, forming conoidal segments to the faces of the bills, and appearing to be the remains of more regular terraces that have been furrowed or partially destroyed by the mountain torrents.
Although the two upper lines are to be traced on the salient angle of the valley opposite to Glen Turit, they are interrupted and obscured to the very top of it. At this place, it is important to remark, the glen takes a turn so as to form a considerable angle ; the opening of Glen Turit being not far from the re-entering one. At the sa lient angle the lowest line is first seen on the left side, as, on the right, it first occurs at the entrance of Glen Turit; into the wide opening of which it runs, together with the two upper ones, for a very short space; the whole of them speedily disappearing on this side of that glen ; while, on the contrary one, the upper line runs with a well marked course till its career is interrupted by the gradual rise of' the bottom or the valley.