410 PHOCEEDINGS OP THE GEOLOGICAL SOCIETY. [June 19, 



into which it passes upwards (distinguished in the memoir as ^4'"*), 

 as well as to the break-up and denudation of both of these. The 

 same underlying brick-earth (cc 4') also distinctly passes under the 

 main sheet of the gravel (ce 4:") at Ilford -Station, forming a slight 

 synclinal, of which the two brick-pits of that place are the ex- 

 tremities. 



The disturbances that broke up and elevated the Thames gravel, 

 although giving rise to terraces, present no feature indicative of the 

 uniform elevation of a valley by the general rise of the country, such 

 as has been described to us by Mr. Prestwich in the case of the 

 Somme. The elevations, on the contrary, have been altogether 

 dislocatory and partial, the gravel being elevated on one side of the 

 principal rectilinear throw as much as 116 feet above the present 

 sea-level, and thrown down to almost as great a depth below the 

 Plumstead and Erith marshes. Moreover the chief portion of that 

 arm of the gravel which extends up the Lea valley, and also that 

 portion of the main mass lying between Stratford and Purfleet, 

 have been thrown eocclusively on one side of the present valley, owing 

 to the unequal elevation. A previous section, fig. 5, affords an 

 instance of this in the Lea valley ; and the section last given, fig. 13, 

 indicates the position occupied by the main mass of the gravel be- 

 tween Stratford and Purfleet, as well as the way in which it has 

 been affected by the faulting of the Lower Tertiary deposits. 



In the memoir I have endeavoured to show the process by which, 

 as it appears to me, the gravel has been placed in this position, and 

 the grounds upon which it seems probable that a part, at least, of the 

 gravel beneath the Thames and Lea marshes may be the same as that 

 of the lower terraces (or cc 5 series), although it occupies no terrace, 

 nor possesses any feature to distinguish it. The position of the gravel 

 on the west and north of Woolwich indicates that it has been affected 

 by a part of the disturbances that have imparted so great a local 

 elevation to the Tertiary beds of that district; and it is from this part 

 that a cross line of dislocation appears to start northwards, which has 

 thrown the gravel in one part of the Lea valley exclusively on the 

 west side of the river, as shown in fig. 5, and elevated it to very 

 considerable heights. The line of dislocation referred to passes at 

 Tottenham out of the gravel altogether; so that, just there, the 

 lower-terrace (or x 5) deposits, instead of resting against elevated 

 terraces capped by the main sheet (or oc 4") gravel on both sides, 

 have this on one side only, the opposite being formed by the London 

 Clay of the original valley ; but as the line of dislocation falls within 

 the main sheet, that deposit forms terraces on either side of the 

 lower or fluviatile series. So far as I am aware, that part of the 

 Thames gravel of which portions have been elevated into high ter- 

 races, has not, either in that elevated position, or in the lower posi- 

 tion in which the local character of the disturbances have left the 

 greater part of it, yielded any organic remains whatever. It is from 



♦ The symbols used here are those adopted in the memoir, a series of patchy 

 gravels marking the denudation which, succeeding the Grlacial clay, preceded the 

 Thames gravel being grouped under the symbols x\, x2, and x 3. 



