330 EROSION SIMULATING FRACTURE. 



Wealden district enunciated by Mr. Whitaker, 1 from which it ap- 

 pears that the river valleys are older than the denudation of the Weald. 



5 4 3 a 345 



Fig. 67. General section of the Wealden, showing the probable 



extent of denudation. 



I Hastings sand. 2 Weald clay. 3 Lower greensand. 4 Gault. 5 Upper 

 greensand and Chalk. 



John Phillips' Hypothesis of the Elevation of Land. Newton 

 supposed the spheroid to be homogeneous ; it has been found that 

 this supposition is by no means fitted to fulfil the observed conditions 

 of the problem of the earth's figure. And the irregularities of attrac- 

 tion indicated by the pendulum experiments, and of curvature demon- 

 trated by direct meridional measurements, seem to show that the con- 

 centric masses of the spheroid are not of uniform density. 



This being allowed, there would seem no objection to supposing 

 that the densities along any one radius of the spheroid are variable, 

 by reason of internal movements among the unequally dense parts of 

 the concentric masses, and this would exactly answer the conditions 

 of the geological problem. For the length of any radius of the 

 heterogeneous spheroid would necessarily vary with the densities ; 

 and considering the small proportion of the height of the land above 

 the mean radius of the latitude, it is clear that small internal changes 

 in a length of 4000 miles would easily account for variations on that 

 line to the extent of 1000 feet or yards. This hypothesis would give a 

 gradual and prolonged elevation in some parts and corresponding de- 

 pressions in others ; it would not affect in a sensible degree the astro- 

 nomical elements of the planet, but would change more or less com- 

 pletely its hydrographical boundaries. 



This view is an example of speculation which has no sound logical 

 basis, since we know nothing of internal movements in the earth due to 

 variable density. But the hypothesis has some historical interest as a 

 precursor of the modern doctrine of crumpling as the cause of elevation. 



Disturbances of the Strata. 



Proofs of Dislocation. When strata, originally level, or nearly so, 

 have been raised to high angles of inclination ; when beds, originally 

 continuous, are found to be broken asunder, and their separated por- 

 tions placed in new relations of position, one portion being raised or 

 depressed, or both deranged ; when layers, originally flat, are found 

 to be bent into extraordinary curvatures ; the conclusion is inevitable, 

 that contortions, if not convulsions, have happened in the places 

 where such phenomena occur. 



1 Whitaker, Geol. Mag., vol. iv., 1867. 







