185 



liardor Ijands in the viver-lieds necessarily checking the rate of 

 erosion of tlie softer. 



Bnt wlien these " consequent" rivers lia\'e begun to deepen 

 their heds, tributaries will begin to flow into them along the 

 " strike " of the strata. These are in a more favoured condition 

 for erosion, inasmuch as they can select the rocks they Avill work 

 in, and choose a soft stratum for their operations, while the 

 " consequent " rivers have to take hard and soft as they come. 

 The softer the stratum M'hich the tributary stream is eroding the 

 faster will its work of erosion be done, the larger will it grow, 

 extending its valley lieadAvard and on either bank, and the more it 

 enlarges itself the faster will it tend to grow since the increasing 

 volume of water will all the while be adding to its erosive power. 



Such a stream is termed a " subsequent " stream, and its 

 actual courses Avill not usuallj' be directly at right angles to its 

 " consequent," but M'ill to some extent depend upon the original 

 slope of the ground, and accordingly will as a rule join the 

 " consequent " stream, making a more or less acute angle with 

 its h('ad waters. 



The larger " consequent " rivers M'ill, caderis paribus, deepen 

 their Ijeds faster than the smaller. Therefore their " subsequents," 

 having a steeper slope, will work faster than the " subsequents " 

 of the other. Working in this way the strongest and most rapidly 

 growing '• subsecpient " may in time invade the valley of one of 

 the weaker " conser^uents " and abstract its head waters, carrying 

 them into the strong " consequent " of which it is a tributary. 

 In such a case between "the elbow of capture," and the head of 

 the " lieheaded " stream, which will tend to retreat gradually, an 

 anti-dip stream will be found <lraining liack into the strike valley 

 along the deserted course of the beheaded consecpient, of course in 

 a reversed direction. Sucli a stream is termed by Mr. Davis an 

 " olise(pu^nt " stream. 



Xow, anyone- looking at a map of Yorkshire will oliservc that 

 there are several rivers originating in the Pennines, and flowing 

 eastward or south-eastward. Such are the Aire, the ^A'harfe, the 

 Nidd, the Ure, the Swale, and the Tees. It is supjjosed l)y the 

 geologists of to-day that these represent original con.sequent 

 streams, Avhich at first flowed straight on to the coast, or in 

 some cases probably to a junction with one another far to the east, 

 but have been .successively captured by the Ouse, a powerful 

 " subse(pient " of the Aire-IIumber, wt)rking along the strike of 

 the soft Triassic rocks, with the exception of the Tees, which has 



