'■-396 ANNALS NEW YORK ACADEMY OF SCIENCES 



SUMMAEY OF PaPEES 



Professor de Martonne stated that the Gausses are high limestonef 

 plateaus extending on the southern border of the highlands of central 

 France. It is one of the rare examples of a natural region with a popular 

 name, extending exactly as far as the geological formations which control 

 its physical aspects. Nobody can fail to notice the change in topography 

 when entering the limestone area. Water has disappeared from the sur- 

 face, all valleys have become dry, many are changed into completely 

 closed depressions called "sotch.^' These depressions are the only places 

 where you can find some red soil, and, in the spring, some water; for 

 this reason they are the only inhabited places on the plateaus. Sink 

 holes, called "avens,'' are frequent; they lead to very extensive caverns, 

 showing alternation of domes and narrow galleries, streams with cascades, 

 lakes, splendid stalactites and stalagmites. There are not more than three 

 valleys with water (Tarn, Jonte, Dourbie). Their depths range from 

 500 to 700 meters. Like the Canyon of the Colorado, they are cut in 

 horizontal layers, showing benches in the weak beds (marls of the Lias 

 and Middle Jurassic) and cliffs in the strong beds (more or less dolo- 

 mitic limestone of the Jurassic). The cross-section and the width of the 

 valley depends on the height at which the weak beds appear above the 

 bottom. The total thickness of the Jurassic beds which built the Causses 

 is much greater than the depth of the valleys. They have been dis- 

 located by faults which can be very easily seen on the stony sides of the 

 valleys, but do not ordinarily appear in the topography of the plateau, 

 although the displacement can amount to over several hundred meters. 

 The rugged but nearly level surface of the plateau may be considered as 

 a peneplane^ slightly modified by underground erosion and dissolution. 

 From some well-selected points the continuity of the plateau of the 

 Causses with the rolling surface of the highest summits of the Cevennes 

 (Aigoual, Lozere) appears very clearly. At one point (Col de Perjuret) 

 you can walk across a great fault separating the Jurassic area from the 

 crystalline massif on a nearly level plain, while to the north and to the 

 -south you see subsequent valleys and cuestas developed by recent erosion. 

 At some points on tbe surface of the limestone plateaus old gravels com- 

 ing from crystalline massif may be found. The plateaus of the Causses 

 seem to be a part of the highest and oldest of the three peneplane surfaces 

 shown by Briquet and Demangeon in the central massif of France.- One 



I- 1 agree entirely with the proposal of Prof. D. W. Johnson concerning the substitu- 

 tion of "peneplane" for "peneplain." — B. de M. 



2 A. Demangeon, Le relief du Ivimousln. Ann. de Geographie, 1910, p. 120. A. Bri- 

 quet, Sur la morphologie de la partie mediane et orientale du Massif Central. Ann. de 

 Geographie, 1912, p. 30, et 122. 



