and other Valleys of the East of England, 183 



of the Ouse at Tempsford; that of the Nen at Oundle; and 

 that of the Welland at Duddington. 



A long list of such concurrences might be adduced ; but my 

 object being brevity, I refer to the annexed Map, and invite the 

 closest and most rigorous comparison of it with the Ordnance 

 sheets ; it is an exact epitome of what will be found there, only 

 that the faint or obscure inequalities and the conspicuous ones 

 are necessarily represented by me alike. The continuation of 

 the arcs through the fens may even in that apparently dead level 

 be distinctly continued or connected by the true test of the river- 

 beds there. 



Although the valleys of the more eastern part of the area 

 mapped derive their force mainly from the denudation that has 

 eroded them, yet it will be found that this denudation has ope- 

 rated according to the direction imparted to it by the configura- 

 tion of surface that I have been describing ; and before adverting 

 to the denudation, I will therefore advert to the causes that 

 have apparently produced this configuration. The aspect pre- 

 sented by both series of circles is such as a pasty or doughy 

 mass spreading by its own weight would take, except that there 

 the diverging circle would be singular, and not repeated succes- 

 sively as we have it here. It appears to me that we have here 

 the result of the yielding of soft strata to the lateral force, 

 caused by the protrusion of a boss of matter from beneath the 

 respective circle-centres. The annexed hypothetical sections of 

 each series will show my meaning. The lateral force exerted 

 would be proportional to the amount of strata elevated and 

 thrown over. Upwards of 4000 feet of strata have been ele- 

 vated over the Isle of Wight centre ; but the greater part of that 

 has resulted from the subsequent and rectilinear movements 

 there that I shall presently notice. On the other hand, we can- 

 not accurately estimate the amount over the Kentish centre : 

 assuming, however, that the whole thickness of the Eocene pre- 

 sent on the Essex side of the Thames was once recumbent 

 over this centre of elevation, the thickness of the displaced 

 strata will not greatly exceed 1000 feet above the sea-level. 

 The lateral pressure thus exerted may be illustrated by the 

 rumpling up of a table-cloth. On the first pressure a wrinkle 

 arises, which reaches its maximum before the next beyond it 

 commences; and that process is repeated as each wrinkle 

 onwards arises ; the greater the rigidity of the cloth, the more 

 speedily do the more distant wrinkles appear. Supposing that 

 pressure to radiate from a centre, the wrinkles would emerge as 

 circles broken as we see those in Somersetshire and Wiltshire. 

 The difficulty in applying such an action to strata consists, 

 among other things, in their immobility and varying rigidity. 



