374 S. 8. Buckman — Rker Development. 



Thames territory. It has come from west of the line of the Welsh 

 backbone, and has broken into the Thames district. A stream such 

 as that marked Z in Fig. 5 would have eaten its way back through 

 the anticlines bounding the Thames Basin, because of its ability to 

 give a quicker fall in a shorter distance ; when it got past the anti- 

 clinal axis and into the soft Trias-Lias territory its course would 

 have been easy. On tbe phenomenon of river-robbery in connection 

 with an anticlinal axis I have given some details in the paper 

 condemned by Mr. Strahan, dealing with the Salisbury Avon and 

 the Pewsey anticline (Proc. Cotteswold Club, 1900, vol. xiii, p. 186). 

 I have there shown that above-ground robbery is not the sole method 

 of conquest ; underground robbery is an important feature, preparing 

 the way for the former. 



One recommendation of the theory which I have very shortly 

 epitomized is that its principles are applicable to all river-systems ; 

 whereas Mr. Strahan's hypothesis would only account for an isolated 

 case. He could not bring in an anticline to account for every strike 

 stream, nor for every case where the water-parting happened to 

 coincide with the escarpment. So he would have to bring forward 

 other hypotheses ; and to have to account for similar phenomena by 

 different hypotheses always seems rather dubious. 



The river-system of the Paris Basin, for instance, can, in the light 

 of the theories of Professor Davis, be read just as easily as that of 

 the Thames, There are the dip streams, such as the Seine and its 

 neighbours, draining from Palaeozoic rocks across the outcrops of the 

 Secondary strata into the Tertiary Basin. Then there is an invader 

 from the outside comparable to the Severn, namely, the Loire, which 

 has broken through the Palaeozoic rocks in the west, has found its 

 way into the Seine area, and has, at Orleans, captured the Upper 

 Loire, which was evidently once a river of the Paris Basin system. 



And now, leaving it to be judged whose theories transgress the 

 limits of legitimate speculation, perhaps I may be allowed in 

 conclusion to pen a few axioms of river development which do not 

 seem to be rightly understood. 



Differentia] denudation has so altered the face of the country that 

 what appears now as an easy course for a river would have been 

 impossible when the river started. 



Escarpments are produced by the removal of material. This is 

 self-evident ; but the logical consequences do not seem to be appre- 

 ciated — that the escarpments were not in existence when the rivers 

 were initiated, and therefore they would not have formed any barrier 

 to the river course, much less the formidable barriers which they 

 now seem. 



Streams which run down a slope or along a sloping trough, that 

 is, dip streams and trough streams, are the only two kinds of rivers 

 that are produced ab initio. Strike streams and anti-dip streams cannot 

 be produced by water running off the original slope ; they are only 

 produced on the secondary slope which results from river erosion, 

 and they have to grow by eating backwards. 



Therefore, the Thames cannot be given a strike course into the 



