59 2 SCIENCE PROGRESS 



The cue which has been missed lies in the recognition of 

 the quasi-permanent character of the chalk massif, and its 

 resistance to disintegration and erosion by frost and rain. 

 One instinctively imagines the chalk that one is familiar with 

 as a soft and friable stone ; but compare the effects of rain 

 on chalk, with a turf covering, and its effects on sandy or 

 clayey strata such as are the outcrops in the Weald, and one 

 will find that the chalk downs are so resistant to the wearing- 

 down processes that they might in comparison be termed 

 " the everlasting hills." 



To this is due their now dominating position over the 

 major portion of the wealden clays and sands, which, prior to 

 the Quaternary period formed heights (calculated by Prestwich 

 to be at least 2,800 ft.) from which fragments were washed 

 down and dispersed over the present summits of the chalk, 

 which at that time constituted the flanks of the wealden range. 

 Or, in other words, these chalk elevations were once only the 

 foot-hills encircling higher mountains. These mountains have 

 melted away under erosive forces, while the chalk plateaus 

 have been able to defy them. 



The proofs of this process are numerous. Shortly stated, 

 they are : 



(1) The absence in the area of the Weald of flints, the pro- 

 duct of the chalk, except in the neighbourhood of the escarp- 

 ments. 



(2) The non-existence of any residual flint deposits on the 

 plateaus and summits such as would undoubtedly result from 

 the removal of the soft parts of the upper chalk. 



(3) The presence of chert and ragstone, and ferruginous 

 sandstone peculiar to the Lower Greensand spread over parts 

 of the highest of the chalk plateaus. 



(4) The perfectly simple history of the ' transverse ' 

 valleys on this assumption. The explanation of these valleys 

 is avowedly a great difficulty with all other theories. 



Again, it is a constant feature in every chalk region that 

 its boundaries are elevated above the bordering strata, gener- 

 ally with the same bold escarpments, which shows that, while 

 other strata suffer from erosion, the turf-covered chalk offers 

 a passive resistance to it. 



It may emphasise the probability of the truth of the fore- 

 going to say that the requisite proofs and ' exhibits ' were 



