XV.-Observations on Roches Moutonnées and other Points of Geological Interest in the Valley of the Urr, Kirkcudbrightshire. By ALEXANDER SOMERVAIL.

Read 17th April 1879.

Topography.-The river Urr, or Orr, as it is not infrequently termed by the inhabitants of its neighbourhood, is one of the principal rivers of Kirkcudbrightshire, having its rise in Loch Urr, a small lake lying on the borders of the adjoining county of Dumfries, which is fed by several streams from the uplands. From its point of issue from the lake it flows in a direction nearly north and south, inclining a little to the eastward, until it falls into the Solway Firth.

The surface aspect of the country watered by the Urr is highly diversified and picturesque. For some miles from its rise its course is rather tame and unattractive; but as it nears Dalbeattie the landscape becomes more interesting, and so continues throughout the rest of its course to the shore at Colvend, where there is some most magnificent cliff scenery (perhaps the finest in the country), with many large caverns, needles'-eyes or natural arches, isolated pillars of rock, deep pot-holes, all cut, carved, and dug out by the action of the waves.

Within this small area almost every type of scenery is to be found, embracing some of the finest effects, of a combination and mingling of both highland and lowland landscape. Of one portion the surface is gently undulating and richly cultivated, while another is wild and desolate in the extreme. In the wild region the lower levels are generally covered with peat-mosses, and everywhere great masses of rock rise above the surface, occasionally so thickly congregated together as to form a scene of the wildest confusion. The hills which bound in the valley also differ much in outline and appearance. For the most part they are huge dome-shaped masses, with well-rounded and smoothed summits; but others are rugged and torn in outline, with jagged and serrated tops, presenting a strange contrast when they come together, as in the case of Bengairn and Screel. Some of the hills are well wooded or covered with verdure, while others are bare from base to summit, with a savage grandeur of their own not surpassed by anything in the North.

It is this great diversity of surface which gives the Urr Valley its peculiar charm. The transition from one class of scenery to another wholly different is frequently sudden and abrupt, sometimes only being divided by the breadth of the river. This

striking change and strong contrast in the surface aspect of the country is entirely due to the nature of the underlying rocks and the manner in which they have been disturbed and affected by erosive agents.

Geological Structure of the Valley.-The whole valley, along with much of the adjoining country, is composed of Silurian strata, among which is intruded a great mass of grey granite, extending from Dalbeattie, where it is largely quarried, to the coast, and spreading east and west over the county, forming some of the principal hills, of which Criffel is the highest.

The granite, although clearly an intrusive mass, is, however, never found to overflow the strata. Excellent junctions of the two rocks are found in various localities, which at their point of contact are both much altered. On Screel there are many fine sections of this kind, and on its very summit there is a curious exhibition of the granite, occurring in small pockets or cavities among the strata which form the hill, without any apparent passage or connection between them, and of the strata in its turn assuming a very granitoid aspect, the two mingling in such a bewildering manner as to shake one's confidence in the igneous origin of the granite.

Formations of more recent origin, such as the boulder-clay, brick-clay, and river-drift, occur at lower levels in this valley. The boulder-clay is not a deposit like the typical till in the Lothians, but a loose earthy deposit, resembling more the remains of old moraine heaps, which is, I think, its true origin. Brickclay occurs at Dalbeattie, in which I found the remains of the hazel, but no marine organisms, as far as I could observe. Above the brick-clays are deposits of sand, gravel, and shingle or riverdrift, occurring at different levels and of different ages.

The whole valley exhibits proofs of extensive denudation, not so observable perhaps over the Silurian as in the granite region, where the river is shut in, and bounded by hills on either side. The sides of the hills, and even their summits, are thickly covered with boulders; the granite hills being frequently capped with masses of Silurian rock and vice versa, all of them belonging to rocks brought down from the higher portions of the valley during the glacial period. No doubt much denudation took place during the glacial epoch; but it would be a mistake, I think, to suppose that the valley had not been excavated long geological ages before that time, and that it had not before then even much of its present configuration. It is only by a study of the geological structure of the Urr Valley that its great diversity of surface aspect, the sudden and abrupt changes in its scenery, the outline of its hills, its dreary, bare, and savage wastes, and its soft and pleasing landscapes, so richly wooded and highly cultivated, become intelligible and easy of interpretation.

Roches Moutonnées in the Valley.-This is a special feature in the Urr Valley. There is no other locality in our country that I am acquainted with where the phenomenon is so well represented; and even among the valleys of the Swiss Alps I have seen nothing to equal it, although ice has been much more recently at work. No one traversing the Urr between Dalbeattie and the coast could fail to note the immense numbers of isolated roundbacked ridges of granite which at every little interval rise above the general surface. So numerous are they that many hundreds of good examples may be counted to right and left of the carriage road, without even deviating from it. They begin in force some little distance north of Dalbeattie, where the Silurian gives place to the granite, and continue to the sea. In a park behind the railway station some excellent examples may be seen; but, indeed, the whole area is so covered with them that it is impossible to cite any locality in preference to another. In form they differ considerably, yet they all conform to one type. They are best described as round-backed elongated ridges, some of them putting us in mind of a boat turned keel uppermost. Their surfaces are smooth and highly polished, some of them wrought into domes and bosses, others rising like a thick rope from the surface, none of them sharp or angular in outline, all rough projections being worn and rubbed down in the most perfect manner. In size they vary from small ridges just peeping above the surface to masses of enormous height and length. From the bottom of the valley they increase in size as they ascend to higher levels, and at last appear to coalesce with the hills which bound the valley, the hills themselves being roches moutonnées on a huge scale.

A first glance or thought would impress the observer with the conviction that the wild confusion of granite ridges held no determinate direction but ran out to every point of the compass. A little careful attention would, however, reveal the fact that the long axis of every individual ridge had precisely the same trend, and that trend was exactly in a line with the trend of the valley. Among other features noticeable in connection with the ridges are the facts that they taper off as they front down the valley, and that all their higher and rougher portions look in an opposite direction, reminding one of the phenomenon of "Crag and Tail" in our own neighbourhood, both doubtless due to the same causes, the differences arising from the nature and relations of the rocks operated on.

Although I made a very careful examination of the surfaces of the roches moutonnées in the granite region, I failed to detect anything I could regard as ice groovings and striæ. I had several excellent opportunities of examining fresh surfaces during the process of tirring for quarrying, and in making a new road to

the railway station, where a large extent of smooth surface of rock was bared of its covering of soil and vegetation, but nothing like glacial striæ presented themselves, although it had been well protected from the action of the atmosphere. I am inclined to think that all striæ, which must have existed at one time, have been removed by the disintegration of the granite, which takes place in spite of a covering of soil and vegetation.

That glacier ice did pass down the valley, there is abundant proof in its higher reaches, where the Silurian rocks are not only highly polished but deeply grooved and striated. The trend of the striæ, as well as the boulders, all point to the conclusion that the glaciers conformed to the present system of valleys in this region as in others.

With regard to the actual amount of work performed by ice, I think we are too sanguine. It is an agent comparatively late of being added to the geological forces, and, like many new things, perhaps too much is claimed for it. It has always occurred to me that its dynamic power is much less than that of water, and that it is so much force partially locked up. It has become customary to speak of it as giving our country its flowing outline, our hills being, it is said, moulded by ice; but much more of the flowing outline of our land, and the rounded form of our hills are, I think, due to the specific rocks which form them acted on by the ordinary operation of the atmosphere. Thus we find that, in form, many hills are dome-shaped, some conical, and others serrated, and that there is a close connection between their shape and their mineral composition.

Whilst fully admitting that ice, in the form of a glacier, has passed down the Urr valley, and has left much to attest its movement, such as striæ, moraine matter, and boulders,-yet I think that it is too much to affirm that these peculiar ridges are en masse the work of ice. Ice has certainly at one period passed over their surfaces, but they are not in toto the product of the glacier,-long geological ages before the glacial epoch they must have existed as a necessary consequence of the erosion of the valley by running water. It is also interesting to note the fact that, independently of ice action, the granite has the tendency to disintegrate into smooth bossy surfaces, an aspect which characterises all the hills of the Urr Valley up to their very

summits.

XVI. On the Connection between Geology, Meteorology, and Agriculture, as illustrated by the leading Agricultural Districts of Scotland. By RALPH RICHARDSON, F.R.S.E., Honorary Secretary of the Society; Member of the Scottish Meteorological, and Highland and Agricultural Societies.

Read 20th May 1879.

It has long been a favourite axiom among writers on agriculture that a very close connection exists between geology and agriculture. Of course, in so far as the agricultural soil falls within the province of geology, there can be no question as to the connection between the two sciences. But what most agricultural writers lay down or infer is that a knowledge of rocks will give a knowledge of the soils produced by these rocks; that one rock produces a bad soil and another rock a good soil; that we may predict with some degree of certainty that a certain rock will always produce a certain soil, and so on. Now, there is no doubt that certain geological deposits will always be associated agriculturally with certain soils. It would be difficult to conceive, for instance, that sand would ever produce anything but a light, dry soil; gravel, a porous soil; glacial clay, a heavy, cold, and wet soil. Agricultural writers, however, often push their conclusions beyond such evident facts. The geological deposits I have just named are neither rocks in situ, nor are they necessarily immediately derived from the rocks in situ over which they lie. They consist of transported material, and bear perhaps no relation whatever to the immediately underlying rocks. The soils to which the agricultural writers specially refer as evidence that various rocks produce various soils, are soils produced by the disintegration of the immediately underlying rocks. A knowledge of geology is counselled the young agriculturist, in order that, to whatever part of the globe he may go, and under whatever climatic conditions he may find himself, he may, from a knowledge of the geology of a district, predicate with safety the agricultural value of the district.

Thus, Professor Johnston says in his well-known "Lectures on Agricultural Chemistry and Geology" (Edinburgh, 1844, p. 354), "If not every stratum, at least every series of strata, exhibits distinguishing and characteristic peculiarities, by means of which it may be more or less readily recognised. On these peculiarities the special agricultural capabilities of those parts of the globe in which each series of beds occurs are in a great degree dependent. "This peculiar character," he adds, "is also more or less con