Drift-beds of the North-west of England and North Wales. 61 



to the contained shells. Since that time he has been diligently col- 

 lecting information to enable him to treat of the nature, origin, and 

 stratigraphy of the Drift lying between Liverpool and St. Bees, and 

 Liverpool and Caernarvonshire. He finds that, in the basin of the 

 river Mersey, the Triassic rocks underlying the low-level Boulder- 

 clay and sands are cut up by a system of preglacial valleys, in some 

 cases presenting very precipitous sides and not in all. cases following 

 the present course of the rivers. If the mantle of clay and sands 

 could be stripped off, we should have scenery differing considerably 

 from the present surface-features. These preglacial valleys are, in 

 parts of their courses, considerably below the present low-water 

 level. 



Where the rock has been bared and is of a nature capable of 

 retaining striations, we almost invariably find it planed and grooved 

 in a direction approximately from N.W. ; and when the rock is 

 soft, it is broken up into rubble and red sand. 



Upon this debris of the Trias lie the low-level Boulder-clay and 

 sands of the plains, the clay lying immediately on the rock being 

 frequently, but not invariably, of a sandier and harder nature than 

 the upper beds. Lines of erosion of a local nature, but often of con- 

 siderable extent, often occur at the top of this clay and then die 

 out ; or there are thin or thick beds of sand and gravel intercalated 

 at the junction and also dying out. Sometimes sand and gravels 

 underlie this harder clay ; but the larger mass of the low-level 

 clay is of a more plastic nature, and is used in brickmaking. Inter- 

 calated sand-beds also occur in this ; and sometimes the clay gets 

 stonier again near the top. 



If we trace the drift from the sea up each river-valley to the high 

 lands, we see at once that the nature of the clay gets more intimately 

 connected with the rocks in the basin above. This is specially 

 noticeable in the Eibble valley, where the brown marine Boulder- 

 clay gradually, above Milton Bridge, gets replaced by a drift com- 

 posed almost wholly of the debris and grin dings of the Carbo- 

 niferous limestone and grits above. In the mountain -districts, 

 also, the drift becomes more localized both in Cumberland and 

 Wales. 



The author's conclusions are that an ice-sheet, radiating from the 

 mountain-district of the English lakes and the south of Scotland, 

 produced the planing and grooving of the rock and the red sand and 

 rubble debris ; then the ice melted back into local glaciers, and the 

 submergence began. The low-level Boulder-clay and sands were, 

 during a slow submergence, laid down probably at depths of from 

 200 to 300 feet ; and the author considers that all the phenomena 

 can be satisfactorily accounted for by ordinary river-action and 

 fraying of the coasts by the sea, combined with frost and ice due 

 to a severer climate bringing down the materials of such river- 

 basins to the sea, while icebergs and coast-ice sailed over, dropping 

 on the sea-bottom their burdens of erratic stones and other materials 

 from the mountain-districts of the north. He pointed out, also, 

 that the great majority of the well-glaciated rocks were specially 



