Apeil 23, 1897.] 



SCIENCE. 



645 



as follows: The Chalk, although nearly hori- 

 zontal, sympathizes with the arching of 

 the Portland oolites in the Upper Jurassic, 

 the Lower Cretaceous, and the Gault series, 

 which formations make up the half-dome 

 as at present revealed by denudation ; and 

 the Chalk is also faulted with the other 

 Mesozoic rocks.* The second reason for 

 .regarding the remarkably even upland of 

 the Chalk as produced by baseleveling after 

 the up-arching and faulting is found in the 

 arrangement of the surrounding streams. 

 The drainage to the southwest of the half- 

 dome, which is the side where the arching 

 is but little broken by faults, likewise shows 

 the influence of the dome form during the 

 initial stages of dissection which followed 

 the uplift of the region. The radiating 

 arrangement of the streams, la Varenne, 

 Cailly, Eobec, le Heron, Andelle and Eple 

 indicates initial and consequent courses 

 upon the western side of the half-dome.j 

 Subsequent branches of the Eple and 

 Bethune have discovered the weaker mem- 

 bers of the Pays de Bray half-dome. In a 

 word, the whole drainage system of the re- 

 gion between the Seine and the English 

 channel is in accordance with what one 

 would expect to find upon an area including 

 a baseleveled half-dome, slightly elevated 

 and dissected to youth or adolescence in the 

 second cycle. Moreover, the adjustment of 

 the drainage to the structure of the half- 

 dome is so perfect that one cannot believe 

 that the elevated region was a gently slop- 

 ing coastal plain upon whose surface conse- 

 quent streams became superposed upon a 

 baseleveled and buried half-dome. The 

 amount of dissection in the present cycle 

 is not sufficient to allow of such perfect ad- 

 justment of stream to structure as we find 

 to-day in the Pays de Bray. 



* See Le Pays de Bray, by Professor A. de Lappa- 

 rent, Paris, 1879, pp. 11, 116, 141. 



t See Neufchatel and Eouen sheets, Nos. 20 and 31, 

 Carte topographique de 1' Etat-Major, 1 : 80,000. 



BLIND VALLKYS AND SINKS. 



If one goes westward from the Pays de 

 Bray, across the exceedingly level upland 

 to the cliff above the straight shoreline of 

 the English channel, where the coast has 

 been developed to maturity by the vigorous 

 actidn of the Atlantic waves cutting into the 

 Cretaceous rocks, he will find remnants of 

 drainage systems left upon the edge of the 

 upland. These remnants appear to have 

 been branches of a river that was situ- 

 ated where the English channel now is 

 found. The remnants are evidently cut 

 by flowing streams of water upon the surface 

 of the land, though at present the valleys 

 descend gently toward the clifl" and there 

 precipitously pitch into the ocean,* and 

 thus evidently depart from the grade of a 

 normally developed one-cycle stream. 



In marked contrast to these evident sub- 

 aerial remnants are the blind valleys seen 

 upon the surface of the upland between the 

 Pays be Bray and the coast, similar to those 

 described in Austria.f One enters a small 

 valley and follows it down for some dis- 

 tance seeing nothing in its form to lead 

 him to suppose that it is anything but a 

 normal branch of some river system. All 

 at once he comes upon a plain area opening 

 out from the comparatively narrow valley. 

 The plain is a sink, surrounded on all sides 

 by higher land sloping gently toward its 

 center. 



A typical young form of sink with three 

 bUnd valleys beginning to develop, working 

 back slowly from the central hole, is shown 

 by M. Mantel in the plan of Mas Eazals.J 

 Slightly older forms are figured by the same 

 writer at Aven de Hures, Igue de Baou, 

 Igne de Planagreze and Pouor de Cettinje.§ 



* See French map 1 : 80,000 ; St. Valery, Abbeville, 

 Yvetot sheets, Nos. 10, 11 and 19. 



t Tietze. Jahrb. k. k. geol. Eeichsanstalt, XXX., 

 1880, 738 ; Supan. Kirchhoff's Landerkunde von En- 

 ropa, 1(2), 1889, 288. 



t Les Abimes, Paris, 1894, p. 184. 



§Loc. cit., pp. 225, 302, 335, 486. 



