SCIENCE 



NEW YOEK, JANUAEY 5, 1894. 



RIVER COURSES IN THE JURA MOUNTAINS. 



BY EMM. DE MARGERIE, PARIS, FRANCE. 



It is well known to readers of Science that Prof. W. 

 M. Davis, in his admirable analysis of the origin of the 

 Vallej^s of Pennsylvania (National Geogr. Mag., Vol. I., 

 No, 3, 1889), started from the assumption of a purely 

 consequent, original course for the rivers which have 

 excavated most of the Appalachian Valleys. As an 

 illustration of such a kind of drainage system existing 

 at the present time the Jura Mountains were given, fol- 

 lowing a statement published by Col. de la Noe and 

 myself in our joint work, "Les Formes du Terrain" 

 (Paris, 18S8). 



More recently, however. Prof. Davis has been led to 

 change this view, according to the results reached by 

 Mr. Aug. F. Foerste, in his valuable account of "The 

 Drainage of the Bernese Jura" (Proc. Boston Soc. Nat. 

 Hist., Vol. XXV., p. 392-420, 1892). 



While admitting that Mr. Foerste has clearly shown 

 that the River Birse could not have taken its present 

 path if it had been a purely original consequent stream, 

 I cannot agree with him when he endeavors to show 

 that recourse must, of necessity, be had to the postulate 

 of an antecedent origin ; for it seems highly improbable 

 that such a small river, whose upper drainage area is of 

 so little extent, could have victoriously reinted the up- 

 lift of such great anticlinals as the Graitery, the 

 Raimeux, the Roche and the Choindez folds are. The 

 failure of other explanations to meet the facts, which is 

 given by Mr. Foerste, together -with the systematic ar- 

 rangement of several series of cluses in straight lines, as 

 the main support of the theory of an antecedent origin 

 (loc. cit., p. 411), does not seem to constitute a valid 

 argument: are we absolutely certain not to have over- 

 looked some possibility, which could turn out, when fol- 

 lowed out in detail, to involve the true explanation ? 



But, apart from these considerations, if such is really 

 the origin of the Cirques followed by the Birse, we 

 should expect to find in the Jura Mountains many ether 

 examples of the same absence of relation between river- 

 courses and constructional form. In order to test in a 

 definite manner the validity of Mr. Foerste's conclu- 

 sions, and to see whether his theory may be of general 

 application in the Jura or not, my friend. Col. de la 

 Noe, has lately drawn, at my request, a large map of 

 the whole country between Bale, on the Rhine, and 

 Belley, near the Rhone, a map upon which all the 

 heights have been referred to a common datum plane 

 (in a stratigraphical sense), viz. : the limit between the 

 uppermost Jurassic beds and the base of the Cretaceous 

 (Neocomien); as a basis for the work, use was made of 

 the sheets of the new map of France, drawn in contours 

 with 20 inetres vertical interval on the scale of 

 1:200,000, geological boundaries being adjusted on the 

 same from the detailed maps of the French and Swiss 

 Surveys. The altitude reached at any point by the 

 horizon selected, above the present surface, if denuded, 

 or underground, if covered by more recent deposits. 



could be computed with a fair degree of approximation 

 thanks to the numerous measurements of sections pub- 

 lished during the last decade for various parts of 

 the Jura; contours were then constructed, every 100 

 metres apart, without any regard to the present topog- 

 raphy, and a photographic proof of the map, reduced 

 one-half, colored in the manner of an ordinary hypso- 

 metric map.'^ 



The result is very striking: nearly everywhere a 

 strict accordance is shown to exist between the actual 

 courses of rivers and the distribution of the lowest parts 

 of the constructional surface; the larger streams, those 

 which might be expected to exhibit the most irregular 

 courses if the assumption of an antecedent ■ origin was 

 correct, are precisely those which follow the most close- 

 ly synclinal depressions, making use here and there of 

 cols where anticlinal arches are locally lowered in a 

 tran,sverse direction. Such is the case for the river 

 Ain, the longest among the tributaries which the Rhone 

 receives from the Jura, and for the Doubs, the longest 

 stream in the whole region. A beautiful illustration of 

 a series of cluses arranged in a straight line, and demon- 

 strably correlated with the lowering of several adjacent 

 anticlines from both sides, is given by the river Bienne 

 between the town of St. Claude and its junction with 

 the Ain. Many other cases might be pointed out to 

 the same effect, viz. : that the Jura drainage, as a 

 whole, is typically consequent upon the deformations, 

 and that, accordingly. Professor Davis was quite right in 

 postulating as the initial stage, in the development of 

 Pennsylvania rivers, essentially original courses during 

 Permian time. 



As to the special case of the Birse, no doubt that ap- 

 parent exception remains to be explained ; that back- 

 ward erosion may have been concerned in the produc- 

 tion of the Bernese Cirques, Mr. Foerste himself seems 

 to concede, in alluding to the Cremine cirque; and I 

 believe' nobody can have seen the Soulce depression, on 

 the outside of the Choindez fold, or the great ravine 

 south of Chatillon, a little more to the east, without be- 

 ing struck by the analogy of both features with an un- 

 perfected cluse — and their purely regressive origin is 

 beyond question. 



A last word about the crystalline pebbles in the Ter- 

 tiaries of the Bernese Jura: Mr. Foerste, following J. 

 B. Greppin, believes that they came from the Schwartz- 

 wald, to the north of the district. But that conclu- 

 sion is far from certain. Dr. Rollier, who has care- 

 fully surveyed the district on the scale of 1:25,000 



'The mc-tbo.l here described does not seem to have been, as yet, appreci- 

 atci: I" I s irll viilue. Originated, I believe, in America, with Professor 

 I.L^Ii 'I ~. nnd splendidly applied to the study of the anthracite fields 



of I' i Ijy his lamented assistant, the late Charles A. Ashburner 



iLlKi :jjl:: ■:■ Ikile resorted to, outside of verv limit.--. 1 districts and for 

 purely scientific purposes. So tar as I am awan , ' . . .1, ^ „,ikir attempts 

 yet made to construct in contour-lines stercograi cinents, for a 



"lad seograpnical area, are Mr Doll us's "Can. .. : :.| u.- de la Sur- 



"-'"'■■"-"•'■■'—■'"'-■ -■■■■■ Paris.", ,n1h..- , , .^ , '. -M'nblished 



"''- . ':^'' .'.;;.■.,.,; I. ali.1 the two 



I i ■ I . '.'1 *.)hi. . ami Indiana, 



■-;.■.■ .. i::^hth and Eleventh 



I . . I.. ■ , . a: bui-vey, rcspcciively. I 

 mysi- :■ ...1,11 :;;., ,■,.■... ,! . . .: , ,. ., .. ..i!..ur map, still unpublished, 

 sh" I'. .. ii.lstone in western Colorado 



(fr ! , ': ~ , : I ,-. the same agreement between 



striii ; .11. ■•:.'] '■. . ■;'■:;;..., ..^ ' - .... I c a..:\ ...:j'_.jd for the Jura was plainly ex- 

 hibited. Tiic CM,islructi..n i.f such mai'swould be specially fitting in those 

 countries where detailed geological surveys are conducted upon topograph- 

 ical maps in contours as a basis, such as are in most parts of tjermany. 



de la Craie dans le H. 

 in Kulletin No. 14 of the 1' 

 maps iilus' rating the sha.j 

 publi hed by Professor u 

 Annual Rep'.. its ..f the I' 



