4: Geology. 



carved out of the London Clay, the preservation of the summit 

 (over 400 feet above Ordnance Datum) being probably aided by 

 the capping of gravel. 



Other signs of subaerial erosive forces, chiefly streams, are given 

 by the valleys, cut through the various members of the Tertiary 

 Series, and sometimes down into the Chalk. It is only for a very 

 short distance on the south, indeed, that our district is not bordered 

 by valleys. 



Southward, the Chalk crops out from beneath the Tertiary beds, 

 and we then reach the long dip-slope of that formation. 



With the exception then of the marsh-flats, the features of the 

 district are due to erosion, guided in places by lines of weakness 



2. DEEP-SEATED BEDS. BY R. H. CHANDLER. 



The data relating to the rocks at a great depth in our district 

 are scanty. Only two borings pass right through the Chalk (both 

 at Crossness Sewage Outfall Works) ; but there are three others 

 that must be within about 100 feet of reaching the bottom of the 

 Chalk (at Plumstead Waterworks, at Woolwich Arsenal Labora- 

 tory, and at Woolwich Dockyard Sawmills) passing through the 

 following amounts of Chalk, 563, 544 and 588 or more feet. 



The older boring at Crossness, made in 1869, passed through the 

 Tertiary Beds, the Chalk (646J feet) and the Upper Greensand 

 (12 feet), and then 148 feet into the Gault ; but as the second 

 boring, made in 1877, went deeper, there is no need to say more. 



The following is the section given by the second boring, differing 

 in some details from the first : 



Thickness Depth 

 in feet. in feet 



Alluvium 21 21 



River Gravel 18 39 



Woolwich and Reading Beds 47 86 



ThanetSand 51 137 



Chalk 631 768 



Upper Greensand (probably Chalk Marl in part 



and Gault in part) 65 833 



Gault (clay) 175 1008 



Red Rocks (marl, shale, sandstone) 52 1060 



Probably the thickness of the Chalk is more truly given in the 

 record of the first boring. 



The question of the age of these red rocks has been much debated, 

 as it has a very important bearing upon the possible occurrence of 

 Coal Measures ; for if these rocks are of New Red age (Triassic), coal 



