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LABOUR MANDATES.

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A DAKOTA DIVORCE ! »

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THE ALLEGED FRAUD ON THE HEARTS…

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Russia and Welsh Coal

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I THE BANK OF MONTREAL

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THE LANDSLIDE j

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THE LANDSLIDE j DUE TO NATURAL EARTH MOVEMENTS. 0 Special Inspection for Western Mail." By Professor W. S. BOULTON I [Professor of Geology at Cardiff University I College]. The origin of the landslides in the Rhym- ney Valley will be better understood by a reference to the accompanying sketch- section across the valley from east to west- showing the positions of some of too places which had been mentioned in the recent accounts of these disturbances. It will be seen that the strata hereabouts are made of the hard Pennant sandstone, or grit, at the base of which is the Tillery, or Brithdir, coal seam, overlying the lower' steam coal series, mostly shales with hard I grit or sandstone bands in their upper part. The lower curved line in the section marks the old pre-glacial valley of the Rhymney River, i.e., the valley eroded by rain and river before the ice of the great Ice Age deposited its mantle of boulder clay or gravelly till over a large part of South Wales, and more especially in these uplamd valleys, where it may attain a. thickness of 50ft. or more. On the eastern side of the valley, marked Cafn Rhychdir, is the site of the landslip which occurred about a year ago. This was a great mass of hard Pennant sandstone, which by the gradual and long-continued action of frost and water along the vertical joint-plaaes, running at right angles to the horizontal bedding-planes of the rock, became suddenly dislodged from the pre- cipitous face of the cliff in the old quarry, and fell, burying the Tredegar road and causing considerable damage to the surface works of the New Tredegar Colliery. But the slides on the opposite, or western, side of the valley, which are now causing so much uneasiness, aire of quite another kind, and are more of the nature of a gradual creep, in very different material from the massive Pennant sandstone. The fact is that the road from Tirphil to Pontlottyn runs for some distance on the debris of an old land- slide, or more likely a, succession of land- slides, the last of which. according to some accounts of old inhabitants, occurred about forty years ago. The village of Troedrhiw- fuwch is built upon the same accumulation of debris. This debris in turn rests upon the glacial gravel and boulder clay that in part fills up the old valley (the dotted portion of the section). At the present time this mass of comparatively loose, incoherent material, partly clay or sand and partly stones and large boulders, is in a state of movement downwards and eastwards towards the valley-bottom. No doubt the heavy rains of the last few months have so soaked the material as to make it to some extent plastic, so that it moves slowly downwards like the ice in a glacier, and, ,a,gain like a glacier, it moves differentially, forming crevaeses where the slippage has been sudden and greater than usual. Bearing this in mind, the cracks in the I schools and houses of Troedrhiwfuwoh, and the subsince8 such as that in the garden of the iun, and the dama-ge to water mains and gaspipee, are quite intelligible, and, indeed, what one might expect. At the lower part I of the slope, along the railway line and near the river, the movement is almost entirely a laterad thrust, which has bulged out the stone wall running along the western side of I the railway track, dislocated the Sebastopol Bridge, thrust out the rails towards the river, and bent and twisted the wooden platform, and wrenched asunder the wooden rails lower down the line. In my opinion it is extremely unlikely that the underground workings of the Powell Duffryn Colliery have had anything to do with these movements; nor is it possible that the bed of quicksand" has been a. deter- mining factor. This quicksand is merely the soft graved amd sand in the glacial deposits that floor the valley and cover up the solid rock of the lower steam coal series, and, when saturated with water, would naturally flow laterally if its support be removed, owing to the pressure of the overlying material. This, I take it, is what happened during the boring operations for the New Tredegar Colliery. The whole mass of super- ficial material on which Troedrhiwfuwch and the railway track hereabouts are built, is of the nature of quicksand, with lumps of solid rock embedded in it, provided it is saturated with water, as it appears now to be. Nor is this landslide a very exceptional occurrence in the valleys of South Wales, though, fortunately, they occur at longish intervals, and apparently in the pact with- out any very considerable damage to life or property. A glance at a map of the Govern- ment Geological Survey of this part of the coalfield shows that many landslides have taken place in the past, and, curiously enougili. nearly all have been along the valleys in exactly the same strata, amd under precisely the same conditions as those in the Rhymney Valley. Thus, in the upper part, and on the western side of the Bargoed Taff Valley, in the Ebbw Vach VaJley just south- east of Blaina, and elsewhere, the hard, massive, and well-jointed beds of Pennant sandstone above the Tillery Vein have fallen away from almost vertical cliffs to collect as great ta.lus-slopes on the softer strata of the lower coal measures below the Tillery Vein, and on which, in some cases, as in that under consideration, mining villages have grown up. It must always be remembered that such material is in a state of unstable equilibrium, and, when saturated with water, naturally flows or slides down the slopes towards the bottom of the valley. In some cases, no doubt, as in the foundation of the ilm at Troedrhiwfuwch, an extra big mass of solid rock embedded in this debris has given a false sense of security, for it is obvious that in time such a mass of rock will move with the surrounding softer material. SECTION ACROSS THE RHYMNEY VALLEY AT TROEDRHIWFUWOH. The arrow shows the direction of movement, producing a lateral thrust towards the river, and, in places, a vertical slippage and subsidence.

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