548 Geological Society. 



the many perplexing features which are connected with the position 

 and distribution of the [Middle Glacial formation ; and while they 

 admit that as to one or two of these the theory which they offer 

 affords no explanation, they suggest that the theory of this forma- 

 tion's origin which best meets the case is as follows, viz. : — As the 

 country became resubmerged, and as the valley-glaciers retreated 

 before the advancing sea, the land-ice of the mountain districts of 

 North Britain accumulated and descended into the low grounds, so 

 that by the time East Anglia had become resubmerged to the extent 

 of between 300 and 400 feet, one branch of this ice had reached 

 the borders of the counties of Norfolk, Suffolk, Essex, Herts, and 

 Bedford, plough-" ng out and destroying any Lower Glacial beds that 

 had been deposited over the intervening counties upon which it rested, 

 and over which we ought otherwise, having regard to the depth of 

 the earlier submergence under which they were accumulated, to 

 find them, but do not. The Middle Glacial formation, consisting of 

 sand and gravel, they attribute principally to the action of currents 

 washing out and distributing the morainic material, which was 

 extruded on the sea-bottom by this land-ice — that ice itself, by 

 keeping out the sea over all the country on which it rested (which 

 was then below the sea-level), preventing the deposit of the Middle 

 Glacial in those parts. The termination of this current- action was 

 accompanied by ir creased submergence, and by a gradual retreat of 

 the land-ice northwrrdsto the mountain districts, until Britain was 

 left in the condition of a snow-capped archipelago, from which 

 eventually the snow disappeared and the land emerged. To the 

 moraine extruded from the base of this ice and into deep water they 

 refer the origin of the Upper Glacial Clay, the moraine material 

 remaining partly in the position in which the ice left it, and partly 

 lifted by the bergs which became detached from the ice. Such part 

 of it as was lifted was dropped over the sea-bottom at no great dis- 

 tance from its point of extrusion ; and in that way the marine shells 

 occurring in a seam of sand in the midst of this clay at Dimlington 

 and Bridlington on the Yorkshire coast became imbedded, the 

 mollusca which had established themselves on the surface of this 

 moraine material having been thus smothered under a lifted mass 

 of the same, which was dropped from a berg. The authors point 

 out that precisely in the same way in which the Middle Glacial is 

 found stretching out southwards and eastwards beyond the Upper 

 Glacial Clay in Suffolk and in Herts, and is succeeded by such clay 

 both vertically and horizontally, so does the earlier-formed part of 

 the Upper Glacial Clay, or that with chalk debris, stretch south- 

 wards beyond the later-formed part, or that destitute of such debris, 

 and is succeeded by it, both vertically and horizontally. This, they 

 consider, shows that the Middle and Upper Glacial deposits, which 

 constitute an unbroken succession, were due to the gradually re- 

 ceding position of the land-ice during their accumulation, the se- 

 quence being terminated with the Moel-Tryfaen and Macclesfield 

 gravels, which were accumulated during the disconnexion and 

 gradual disappearance of the ice, and while the laud still continued 

 deeply submerged. 



