572 Correspondence. 



of turf) furrow their faces, and tend to disfigure a smooth slope by 

 a series of unsightly gutters. Frost cannot act effectively where an 

 escarpment or slope does not already exist. Mr. Whitaker, to a 

 certain extent, seems to admit this, when he speaks of " outliers " 

 as " relics " of a former escarpment, and " inliers " as signs of a 

 future escarpment. He invests subaerial agency with a power of 

 beginning, by making something very unlike an escarpment, and 

 ending by ruining an escarpment — the escarpment being only a 

 stage of maximum development. Somewhat like Professor Babbage 

 and his calculating engine, he makes his machinery capable of 

 performing a miracle at a certain stage of its working, so as to give 

 a result the opposite of that preceding and following. The fact 

 would appear to be, that the action of the atmosphere, instead of 

 forming a slope, tends directly to make a pre-existing slope less 

 escarpmental. It has never been satisfactorily shown how, on a 

 plane of marine denudation, the atmosphere could begin the work of 

 escarpment-making. 



Removal of Detritus. — Mr. Whitaker admits the absence of a talus 

 from the face of Chalk escarpments, and states that the solid chalk 

 comes up to the surface. But this is the case, not only with the 

 slopes but with the hase of many Chalk escarpments ; and it may be 

 asked, if rain has washed away the soluble chalk, what has become 

 of the insoluble flints ? Is it reasonable to suppose that rain and 

 frost, which act intermittingly, or by successive stages, can leave no 

 sign of their action? Col. Greenwood (the father of modern sub- 

 aerialism) admits that one rain leaves soil on its path to wait for the 

 " next rain." The entire absence of detritus implies a cause equal 

 in force and volume to a " sweeping " removal of the mass of chalk 

 necessary to leave an escarpment. Uniformly-cut, and cleanly swej)t 

 surfaces of chalk are common not only on the face and at the base 

 of escarpments, but on the sides of gently swelling eminences, and 

 on the level summits of table-lands, or " planes of marine denu- 

 dation." There are many short Chalk escarpments, and parts of 

 long escarpments, where the ground at the base is a plain, and 

 where there is no stream to carry away the detritus which must 

 result from the action of rain and frost, if they act at all. The 

 streams in the neighbourhood of other escarpments are so sluggish, 

 and choked with vegetation, that they tend rather to raise than 

 lower the level of the area through which they flow. Mr. Whitaker 

 admits that the formation of some escarpments is " delayed," and 

 that rains, during a " former order of things," must have been more 

 powerful than now. Why, then, not allow the advocate of marine 

 denudation to suppose the action of currents formerly more energetic 

 than at present ? He appeals to the destruction of forests and other 

 changes introduced by man as diminishing the fall of rain ; but it 

 is obvious that the denuding action of rain is much increased by the 

 removal of trees,^ and the cultivation of the soil. 



Inclined 'Escarpments. — Mr. WMtaker refers to escarpments, the 

 base of which at one place is higher than the top at another ; but 

 ^ See Ljell on North American forests. 



