TRANSACTIONS OF SECTION E. 723 



Urals) a complex: of two chains running N.W. in the centre (Schrader's ^lap), and 

 two chains running N.E. on both ends of the main massif; while the Sierras de 

 Estrella, de Gata, de Gredos, and Guadarrama, and the chains of Sierra Morena of 

 Murcia and Granada assume the N.E. direction. The central plateau of France 

 and the mountains of Scotland are again instances in point. 



Of course these two directions are not exclusive. The eastern Tian Shan 

 some mountains of Minusinsk, and, may be, the Balkans are instances of the W. to 

 E. direction, and faint traces of meridional upheavals (which may continue even now 

 to be going on) may be indicated. Chains en echelon (Spain, North Asia) must also 

 be mentioned ; as also curved border ridges grown on the edges of plateaus, espe- 

 cially along the N.W. border of the high plateaus of Asia, where the deepest 

 depressions lie at its borders (southern shore of Caspian, Lake Baikal). Various 

 causes may contribute to produce this growth of mountains along the edo-es of 

 plateaus, especially if these chains have originated at a period when the 

 plateaus were continents surrounded by the ocean. 



The fact that the two great plateaus of Asia and North America — the two 

 oldest backbones of the two continents — converge towards Behring Strait, in the 

 same way as at the present time the continents have their narrow extremities 

 pointing towards the South Pole, deserves a special attention. This fact may be 

 one more confirmation of the hypotheses which look for general telluric, or even 

 perhaps cosmical causes in order to explain the origin of mountains altoo-ether. 



4. PotamoJogij as a Branch of Physical Geographij. 

 By Professor Albrecht Penck, Vienna. 



The paper shows the necessity of a profound study of rivers as a department of 

 physical geography, equivalent to oceanography and limnology. This branch may 

 be called potamoloffy. It can be treated under five different heads — 



1. The physics of running water. 



'2. The bulk of water and its fluctuations. 



3. The action of water on its bed. 



4. The distribution of rivers on the earth. 

 o. The rivers as a scene of organic life. 



The author points out that the physics of running water are not known to such 

 a degi-ee that a formula for the mean velocity could be established, the existing 

 ones being in general incorrect. He farther gives an account of some new results 

 obtained by him concerning the bulk of water of Central European rivers and its 

 relation to precipitation; he expresses the wish that measurements of the quantity 

 of water of the larger rivers should be undertaken, and that the results of gauo-e- 

 observations should be published in a regular way, as are the results of meteoro- 

 logical observations. He proves the necessity of studying the movement of river 

 gravels, and of publishing maps of river-bottoms. He shows that there is still a 

 want of exact knowledge of the magnitude of river-basins and river-lengths of 

 European and North American rivers, and refers to some difficulties in determinino- 

 those quantities. As to rivers which by climatic causes are not constantly 

 running, he agrees that extreme values of their catchment basins and lengths 

 should be determined. AVhile acknowledging what had been already done for the 

 study of ■ rivers for practical purposes (irrigation, floods, navigation), he holds that 

 much remains to be done in order to establish a scientific potamology. 



5. Geographical Development of the Lower Mississipin. 



By E. L. CORTHILL. 



3a2 



