Ransome.] 



The Great Valley. 



393 



In the middle of the same year (1883) a paper appeared in 

 England by Dr. Ricketts,* in which he calls attention to the lack of 

 interest taken in the question whether sedimentation is the cause of 

 subsidence or vice versa, and refers to an earlier paper published in 

 1872.1 He favors the former view, but brings little to its support. 



A month later Gardner % published a paper in "Nature," in 

 which lie also regards the earth's crust as being highly sensitive to 

 superficial loading, as shown by the subsidence of delta-deposits in 

 particular. He also gives considerable prominence to the supposed 

 effect of pressure in producing a fusion and viscosity of the deeply 

 buried lower beds. 



This paper was the immediate cause of a considerable corre- 

 spondence on the subject in the pages of "Nature" during this and 

 the following year, which, although of a rather desultory character, 

 brought out a few points which may be worth noting in this place. 

 Mackie § points out that if subsidence be due to loading of sediment, 

 then it should continue indefinitely. He considers that it is due to 

 tangential pressure acting upon a portion of the crust that has been 

 thickened by sediment and thereby rendered more resistant. The 

 area of deposition becomes a geosyncline. Gardner || carries the 

 idea of a sensitive crust so far as to believe that the removal of 

 weight by erosion along a sea-cliff causes a local elevation which 

 results in giving the strata exposed in the cliff a prevailing landward 

 dip. Ricketts Tf suggests that the height of ordinary hills maybe 

 largely due to lightening through denudation. Singtonft i s opposed 

 to such views of a sensitive crust, and says that ''every formation 

 appears to contain evidence that subsidence took place independently 

 of deposition, and elevation independently of denudation." He 

 cites the case in which 5,000 feet of limestone is succeeded by grits 

 and shales in Derbyshire, indicating a rise of the sea bottom pre- 



* Oscillations of the Earth's Crust, Geo log. Mag., Vol. XX, p. 302. 

 fGeol. Mag., Vol. XIX, p. 119. 



J Elevations and Subsidences: Or the Permanence of Oceans and Conti- 

 nents. Nature, Vol. XXVIII, pp. 323-327. 

 \ Ibid, p. 488. 

 || Ibid, pp. 488, 489. 

 If Ibid, pp. 539, 540. 

 n Ibid, p. 587. 



