Wood — On the East Essex Gravels. 403 



Thames moutli on the north Kside, and in those through which the 

 Crouch passes above Cricksea ; and especially in the deeply-scoured 

 Upper Valley of the Crouch and Valley of the Blackwater Estuary ; 

 and in the formation of the ridge from Althorne to Stow-Mary, 

 which has divided these valleys, and formed them out of one original 

 valley into their present separate condition. 



1 must, ask my readers once more to look at the Map, and to 

 observe that the trumpet-shaped openings by Snodlandl and Otford 

 are, after all, only the continuations of the great curvilinear trough 

 which forms the Upper Valley of the Crouch, and the valley of the 

 Blackwater Estuary. The original inequality of surface, imparted 

 by the forces causing the elevation of the Boulder-clay (or Upper 

 Drift) sea, has taken this symmetrically curved form; the symmetric 

 repetitions of the curves, shown on the Map, cutting through the 

 Boulder-clay as far as Eutlandshire.^ Of the powerful (earthquake) 

 wave-like lateral thrust, giving rise to these inequalities we have an 

 example in the ridges intersected by Section 9. It is the deepening 

 effect of denudation that has made these troughs so conspicuous in 

 some places to what they are in others. This denudation has been great 

 in the valleys of the Blackwater Estuary and Upper Valley of the 

 Crouch, but far greater in the trumpet shaped mouths of Snodland 

 and Otford. The excessive scour of the eastern part of the Weald — 

 whose direction transverse to these older curvilinear troughs has 

 been (west of Maidstone) induced by the rectilinear direction of the 

 movements that succeeded the Thames gravel — has almost obliterated 

 the curves in the Weald Valley, but they re-appear in the less de- 

 nuded area of the South Downs. These curves are only one set of 

 a numerous and intricately inosculating series that extend not merely 

 over the whole of the area south of Flamborough head, occupied by 

 deposits from the Lias upwards, but also over the area occiipied by 

 similar deposits in Prance.^ Some of those, originating far away in 

 France, can be traced into England, and into inosculation with those 

 that, in so marked a manner, cut through the Boulder-clay and 

 Middle Drift here. Their uitricate connection with each other, were 

 their system shown on a map, would satisfy, I think, any observer of 

 the unity and contemporaniety of their origin ; while the relation 

 they bear in this country to the Boulder-clay shows them to have 

 originated subsequently to that deposit, and before the formation of 

 the Thames gravel ; in a word, shows them to have originated under 

 the Boulder-clay sea, and by denudation during its emergence. 

 This fact, with the structure of the gravel beds, which in these 

 papers, I have been endeavouring to elucidate, and the features of 

 the denudation that has accompanied them, does, in my mind, point 



' Of these arcs cutting through the drift, the repetitions of the arcs forming the 

 curved valleys (shown in Division 1 of the Map), the principal is that extending from 

 Eeading to Hitchin. The symmetrical coincidence of this arc, and the cut which 

 (between Hemel Hempstead and Royston) it makes through the Upper and Middle 

 Drift, may be seen in the small sketch Map in Division 3. The next great repetition 

 is the arc by Market Harboro, Rockingham, etc., which cuts in a similar way through 

 the Upper Drift, capping the heights between those places. 



2 I have carefully extracted them all from the French Ordnance Maps. 



