364 



PLEISTOCENE GEOLOGY OF THE THAMES VALI-EY. 



There is one valley to which it is necessary to refer in some 

 detail, namely, that occurring to the west of Hangman's Wood. 

 Its direction is north and south, its southern end opening out into 

 the lower ground formed by the Brickearth and Alluvium border- 

 ing the Thames. Its early origin is somewhat obscure owing to 

 the fact that it has been much modified by the Thames in 

 Pleistocene times. This modification has tended to increase 

 both its width and its depth, but more especially the latter, the 

 result being that the High Terrace Gravel which formed its 

 floor has been swept out together with part of the underlying 

 Thanet Sand. Slightly to the west of the mouth of this valley a 

 good section is to be seen exposed in the " Globe " brickfield, 

 near Little Thurrock. This section shows how this deepening 

 was accomplished. Here the Thanet Sand has had its surface 



Fig. 4. Section in the " Globe Works " Pit east of Grays, i, Brickearth ; 



2, Brickearth and Gravel Interstratified (Middle Terrace Series) ; 3, Gravel 



and Sand washed down from Valley to the North (High Terrace Series 



derived) ; 4, Thanet Sand. 



eroded by the mechanical process of gravel being swept over it, 

 and upon this eroded surface a mi.\ture of well stratified detritus 

 derived from the High Terrace Gravel and the Thanet Sand 

 reposes, the dip of which is to the south the angle of inclination 

 being similar to that of the floor of the valley. Upon this re- 

 arranged material the Middle Terrace Brickearths have been 

 laid. It is, therefore, clear that the deepening and widening of 

 this valley took place during the time which ensued between the 

 end of the High Terrace stage and the deposition of the earliest 

 sediments of the Middle Terrace (Fig. 4). 



From these facts it is safe, in our opinion, to regard the 

 valleys referred to as being the result of the solvent action of 



