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Origin of the Terraces, Balks, or Lynchets of the Chalk Downs.

D

By G. POULETT SCROPE, F.R.S., F.G.S., &c.

F the natural features of the county of Wilts, none perhaps

are so prominent as its chalk downs. And they have consequently attracted considerable notice from our local historians and naturalists, from Aubrey down to the latest contributors to this Magazine, in the last number of which alone two articles describe their ancient earthworks and general character. But I have vainly looked in any of these publications for a descriptive account of what I consider to be some of the most remarkable features of these chalk hills, viz.; the numerous terraces, locally called balks (banks ?) or lynchets (ledges ?), which frequently score their slopes in more or less horizontal lines. These terraces are perhaps most conspicuous between Mere and Hindon, and near to Warminster and Market Lavington, but are indeed to be met with almost wherever the chalk downs slope into the valleys or low plains. No one travelling along the high roads which run at

the foot of these slopes, can have failed to notice them contouring round the projecting headlands and far up into the intervening combs; and few can have done so without forming some theory as to their origin. I had myself entertained no doubt as to their artificial production, but a few years since I was startled by reading in a scientific Journal an article written by Mr. D. Mackintosh, F.G.S., announcing the opinion that these terraces "thousands in number, are so many raised sea-beaches," left at the height where they now stand by the waves during the progress of excavation by the sea of the valleys in which they occur. (“Geological Magazine,” vol. iii., p. 69.) I took the liberty of opposing this view, which I considered perfectly preposterous, in a communication printed in the same Journal ("Geological Magazine," vol. iii., p. 293); and as the subject will probably possess some interest to Wiltshiremen, the following extracts from that paper may be acceptable to the readers of this Magazine:

"Any one who lives in a neighbourhood where these banks occur may see them, if not in course of formation from their beginning, yet growing yearly before his eyes wherever the hill-slope above is under arable cultivation. In this case as the course of the plough almost always follows the more or less horizontal tread of the surface (which is also the direction of the banks), the ridge of soil raised by the mould-board of the plough has everywhere a tendency, through the action of gravity upon it, to fall down-hill rather than upwards. This down-hill tendency of the disturbed soil is greatly assisted by the wash of heavy rains upon the loosened materials of the sloping surface; and the result is that year by year the whole surface soil of the slope, when under continuous arable culture, is, slowly indeed but surely, travelling downwards, until it is stopped either by the cessation in that direction of the disturbing action of the plough, or by some hedge, or wall, or bank, which limits this. Hence it is that wherever a hedge or wall forms the lower limit of any arable surface possessing a considerable inclination, an accumulation of mould or made-earth will be found on the upper side, often several feet in depth, and forming a bank by that much elevated above the surface of the soil on

the lower side of the fence. In the meantime the upper parts of the slope losing their vegetable mould get poorer and poorer; the plough works nearer the bone (as the farmers say) and the soil is then only recruited by contributions drawn from the subsoil or triturated rock beneath. The thrifty farmers of Devonshire therefore often employ their idle hands and teams in winter in digging out the soil which has descended to the bottom of their steep fields, and carting it up to the top again; thus restoring the balance, and maintaining the fertility of the upper portion.

But it may be said the ordinary lynchets of the chalk downs have no hedge or wall along their lower boundary which might act as a material obstacle to the descent of the soil before it reaches the very bottom of the comb or vale. True; but it may be said in reply that fences possibly existed there in early times. It is, however, in no degree necessary to suppose this in order to account for the origin of the banks, which in fact where a fence does exist will rarely be found in actual contact with it, but stopping short by a yard or two above it, at the point where the action of the plough ceases.

We know that in early times the arable lands of the greater part of England were held in severalty by different tenants or owners; and also that on the common field system nothing was more usual than for the same owner or occupier to cultivate several distinct strips or breadths of land separated from each other by the lands of others. Let us assume that a hill side was held in three or four strips of land lying one above the other by distinct occupiers: the strips having, for the sake of convenience in ploughing, their greatest length in a horizontal or nearly horizontal direction, following the sweep of the hill side, whether curved or straight. The boundary line between two of these neighbouring strips may have been originally only a mathematical one, connecting say, two mere-stones, and yet a bank will soon have been formed along it, for each upper cultivator will naturally take care not to allow the soil of his strip to descend to fertilize that of his neighbour below. He would draw the lower limit of his strip by a reversed furrow, throwing the last ridge of soil up hill; thus leaving

a slight trench, sufficient however to stop the silt washed down from above, which consequently would accumulate there in a bed perhaps only an inch or two in depth. But in the next year or next ploughing, the process is repeated; the cultivator again checks the descent of silt by a double boundary furrow, or the same effect is produced by the slight edging of earth or grass which forms the lower limit to the action of the plough. And thus by degrees a slight bank of earth is formed which in the progress of years increases into a "lynchet" or "balk," i.e. a steep grassgrown bank, several feet in height, with a somewhat flattened terrace above-separating the parallel strips on a hill-side in the hands of distinct cultivators. Or, indeed, the same result may be purposely produced by the same cultivator, occupying the whole slope, and desirous of stopping the wash of soil down to the bottom of the valley by forming some artificial checks of this kind to it, in the manner of the terraces so laboriously formed by the vinecultivators of southern Europe.

This is not mere theory. I have often watched the growth of such banks, and even witnessed their formation from the beginning. It is noticeable indeed with what rapidity they are produced and increased year by year. For example I have seen one from two to three feet high formed in the course of ten years at the foot of a steep slope first broken up from old pasture at that distance of time. A foot-path runs by the side and below it, but there is no hedge or other material limit to check the wash of the soil downwards, other than the slight ridge of grass that grows on the outward edge of the lowest furrow by the side of the path, which latter remains uncovered and undisturbed. It is evident that the slightest impediment would suffice to check the descent of the silt into the path and cause it to settle above.

This I have no hesitation in asserting to be the simple explanation of the origin of those "thousands of raised sea-beaches from a few inches to several feet in height which may be found in Wiltshire, Dorset, and other counties," according to Mr. D. Mackintosh. Were they ever sea or indeed river-beaches, they would be found composed of shingle or rolled pebbles. If sea or river-worn cliffs,

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