244 0N A DECENT SUBSIDENCE AT MUCKING, ESSEX. 



part of Essex lying south of a line from Purfleet to Stanford-le- 

 Hope. The lowest formation seen is the chalk, which is visible 

 over a considerable part of it as far eastward as Grays and 

 Stifford. Thence to Stanford-le-Hope and East Tilbury it 

 appears only here and there, at the base of the higher ground 

 bordering the marshes south of Little Thurrock and West and 

 East Tilbury. Above the Chalk, with a northerly dip, come the 

 Tertiary formations ; the Thanet Sand, the lowest of them, being 

 the only one now existing south of a line ranging from a point 

 north of Hangman's Wood to Mucking Ford. North of this 

 line the Woolwich and Reading Beds and the Blackheath Beds 

 come on above the Thanet Sand. Then the London Clay (which 

 makes so much of the surface of Essex north of this district) 

 comes on above the other formations mentioned. But it attains 

 but little thickness, and covers but little ground within our area,, 

 though prominent at Horndon-on-the-Hill, just beyond it. 



Later in date than any of the Tertiary formations mentioned,, 

 and of comparatively little thickness, is the old Thames Gravel,, 

 formed ages ago when that river was flowing at a much higher 

 level than at present. The deposition of this bed has been a 

 most important influence in the production of the present 

 physical geography of the district. Here, as higher up the 

 stream, the old course of the Thames was usually northward of 

 that which it now has, the result having been the deposition of 

 River-gravel over most of the surface between Purfleet and 

 Stanford-le-Hope and East Tilbury, the Tertiary formations 

 having been much planed down during the operation. To 

 illustrate the effects of this planing down I may mention the 

 following examples. In the great chalk pit west of the road 

 between Grays and Stifford we find old Thames Gravel with only 

 8ft. of the Thanet Sand between it and the Chalk. Then at 

 Hangman's Wood there is about 46ft. of Thanet Sand between 

 the Chalk below and the Thames Gravel above. At the recent 

 Mucking subsidence there is in all probability a thickness of 

 about 150ft. of Tertiary beds between the surface and the top of 

 the Chalk. And though, owing to its position at the head of a 

 slight valley, there is no old Thames Gravel at the surface of the 

 recent subsidence, there is a broad plateau of it a few yards away 

 both eastward and westward, And in each of these instances 

 the height of the surface of the plateau above ordnance datum is 



