PLEISTOCENE GEOLOGY OF THE THAMES VALLEY 



3^3 



ally descend. The next section to be noticed goes considerably 

 further than this since it shows that in this process lies the true 

 secret of the origin of the valleys. 



Just to the west of Belmont Castle a small north and south 

 valley occurs, the floor of which is at an elevation of from ninety 

 to one hundred feet O.D. Its southern extremity is trancated by 

 the northern face of the Chalk-quarry of the Grays Portland 

 Cement Works which thus affords a good transverse section 

 through it. The surface of the Chalk has been eroded by 

 carbonated water so as to form a groove into which the Thanet 

 Sand and High Terrace Gravel have subsided. Here and there 

 where some portions of the Chalk have offered more resistance 

 to the solvent action than the main bulk small irregularly 



Fig. 3. Section across Valley S.W. of Belmont Castle. 



rounded bosses stick up and protrude into the overlying strata. 

 The axis of this furrow is coincident with that of the valley, both 

 in direction and in longitudinal position, while the general 

 contour of the furrow and that of the valley floor as seen in 

 transverse section are parallel (Fig. 3). 



The section afforded by the northern face of the quarry 

 west of Milwood Lane gives similar evidence of the erosion of 

 the surface of the Chalk into grooves in this district, but the 

 relation of the surface contour to that of the groove is not so 

 apparent here as in the last instance as the ground has been 

 subsequently modified by other subaenal denuding agents to a 

 considerable extent. 



