56 JOURNAL AND PROCEEDINGS 



broad shallow valley has been excavated out of Pleistocene forma- 

 tions in recent days. 



(i) As before stated, the bluff has an elevation of about 80 feet 

 above the plain. The river itself flows from 150 to 300 feet distant 

 from the brow or edge of the bluff, thus producing a more gentle 

 slope than is ordinarily required for clay to withstand the mechani- 

 cal acti( n of weathering forces. The length of the slide is 700 feet, 

 and the approximate width of the original surface fallen, is repre- 

 sented by a plot of ground 165 feet broad, in part, which for a length 

 of 375 feet, has slidden bodily from the face of the bluff, for a dis- 

 tance of fifty feet or more, and sunken from 40 to 60 feet, without 

 further disturbing its grassy surface and forest trees, other than by 

 producing a large longitudinal pressure, and the tilting of the trees 

 a few degrees towards the hillside, with the overthrow of some others. 

 This plot is still about 70 feet distant from the river. At the eastern 

 end, the slide graduates into a confused mass of pyramids of jointed 

 clay, between which there are great fissures. These masses at the 

 eastern end of the landslide, in place of quietly sinking down as at 

 its western end, rolled in confusion from the side of the bluff, not 

 only to the river channel, but 100 feet across it, thus temporarily pro- 

 ducing a dam, which has subsequently been removed by the river. 

 The cause of the landslide is evidently due to hydrostatic force, 

 acting in the vertical joints, along which, and also along the planes 

 of bedding, the clay was eventually softened, and produced slipping 

 surfaces, which yielded to gravity and lateral pressure. 



(2) Whilst beneath the hummocky mass, at the eastern end of the 

 slide, the dynamical effects upon the lower beds of the more or less 

 plastic clay, at the level of the river, are concealed ; yet between the 

 sunken plot of wooded ground and the river, which is about 70 feet 

 distant, these are shown in a most interesting manner. Here we find 

 that the beds of clay are pushed up vertically upon their edges, by a 

 lateral thrust, and that the gravel of the present river, which occurs 

 at only ten feet or more below the surface of the plain, is also lifted 

 up from ten to fifteen feet. These vertical beds can be traced for ,, 



some hundreds of feet longitudinally, and in some places they are I 



more or less distorted. Thiis we see in miniature, the phenomena of 

 upheaval, 'and of deformation of great stratified masses. The dynam- 

 ical forces here, have resulted from an enormous mass sliding sud- 



