976 



SCIENCE, 



[N. S. Vol. XIV. No. 364. 



Tamar in Cornwall (Tavistock sheet) are of this 

 kind. But it is more common to find the 

 streams incompetent to swing steadily around 

 the curves of their meandering valley floors ; 

 the headwaters of the Thames in the Cotswolds 

 ofler striking illustrations of this sort. The 

 Evenlode (Oxford sheet) and the Cher well 

 (Chipping Norton sheet) are typical straggling 

 streams, meandering on so much smaller a scale 

 than their valley that they seem to wander aim- 

 lessly about its curving floor. The chief cause 

 of the incompetence of these streams is probably 

 to be found in their loss of volume, from having 

 been beheaded by the (Stratford) Avon ; yet 

 some additional cause must be looked for, inas- 

 much as the Avon, which should be gaining in 

 volume as its obsequent branches increase in 

 length with the retreat of the Cotswold escarp- 

 ment, is also somewhat incompetent to follow 

 the pattern of its distinctly meandering valley 

 (Worcester and Stratford- on- Avon sheets). No 

 general climatic change towards less rainfall 

 can be appealed to, for the streams cited in 

 Cornwall and Devonshire, as well as certain 

 others in Wales, show no signs of diminished 

 volume by shrinking from the curvature of their 

 valleys. The meanders of the Torridge, above 

 mentioned, are remarkable for their large arc, 

 and for the associated interlocking or dovetail- 

 ing of the upland spurs that enter the valley 

 meanders. The spurs that enter the meanders 

 of the Evenlode valley appear to have been 

 trimmed and steepened on their up-valley side, 

 the result of the systematic down-valley migra- 

 tion of the river meanders before the decrease 

 of volume took place ; the distinctness with 

 which this delicate detail of form is shown being 

 a high tribute to the accuracy of the topograph- 

 er's work. 



HYDROGRAPHY OF THE PARIS BASIN. 



The geological structure of the Paris basin has 

 been minutely studied by Dollfus, who makes 

 application of his results in a discussion of the 

 ' Relations entre la structure geologique du 

 bassin de Paris et son hydrographie ' {Ann. de 

 Oeogr. , XI. , 1900, 313-339, 413-435, map). The 

 Cretaceous and Tertiary strata that occupy most 

 of the basin have been gently undulated in late 

 Tertiary or in post-Tertiary time ; the shallow 



synclines and low anticlines generally run 

 northwest-southeast, in accordance with the 

 trend of the more closely folded underlying 

 Paleozoic strata, which appear in Brittany and 

 elsewhere. The author recognizes several 

 classes of streams : consequent, inconsequent, 

 obsequent (the definition of this term does not 

 agree with that given by others) and secant 

 (traversing an anticline) ; subsequent streams 

 are not explicitly noted. He then shows that 

 many streams of the Paris basin are consequent, 

 inasmuch as they follow synclinal troughs. The 

 Somme is a good example of this class, although 

 it does not drain the whole length of its syncline 

 (p. 317). The eastern part of the syncline is 

 occupied by the Aisne, which is led southward 



8o Kiuowi 



by the Oise, away from what appears to have 

 been its original westward extension to the 

 Somme ; the Oise being secant to several anti- 

 clines on its way to the Seine just below Paris. 

 This diversion is ascribed to capture (p. 318), 

 though the causes and proofs of capture are not 

 clearly set forth. The diversion might possibly 

 be consequent on a rise in the floor of the syn- 

 cline between the Oise and the head of the 

 Somme. 



While many examples of consequent synclinal 

 streams are indicated, they are usually of rela- 

 tively small volume. A number of the larger 

 streams frequently follow oblique courses, seem- 

 ingly indifferent to the anticlines that lie across 

 their way, and for this inconsequent behavior 

 no full explanation is ofiered. The antecedent 

 origin of the Meuse through the Ardennes is 

 discarded (p. 330) on what seems insufllcient 

 evidence ; its gorge is explained as the result 



