688 



SCIENCE. 



[N. S. Vol. IL No. 47. 



back of its delta. The surface of the loess 

 is diversified by valleys of denudation. 

 This peculiar formation is explained as con- 

 sisting neither of glacial flour nor teolian 

 deposits; it is 'plainly stratified,' certainly 

 of aqueous and probably of marine origin ; 

 but in the discussion following the reading 

 of the essay the latter conclusion was dis- 

 puted by several geologists present at the 

 meeting. The outer niai-gin of the loess 

 lowland is an old, rounded sea cliff, with 

 headlands and bays, overlooking the uni- 

 form level of the delta; but details of this 

 interesting geographical feature are unfor- 

 tunately not given. 



RIVEE VALLEYS OF THE HIMALAYAS. 



The occurrence of the chief water part- 

 ing back of the highest range of the Hima- 

 layas has called forth various explanations, 

 to which E. D. Oldham, Superintendent, 

 Geological Survey of India, adds another 

 ( Jl. Manchester Geogr. Soc, ix, 1894, 112- 

 125) . He suggests that the south-flowing 

 rivers have extended their headwaters 

 backward through the main range, by rea- 

 son of their great slope in comparison with 

 the rivers that flow northwards from the 

 ■ mountains to the elevated table-lands of 

 Thibet. The contrasted river slopes on the 

 two sides of the present main divide are il- 

 lustrated by a well drawn section. The 

 author points out that the divides thus 

 shifted away from the axis of the range al- 

 ways provide low passes through the moun- 

 tains, because the former high slopes of the 

 axial divide have been obliterated. [Heim 

 describes terrace-like remnants of the upper 

 parts of beheaded vallej'S in cases of this 

 kind in the Alps, overlooking the deepened 

 valley of the beheading stream; but no men- 

 tion of these details is made by Oldham.] 

 The larger rivers are thought to be antece- 

 dent to the out ranges of the Himalayas, 

 across which they have cut profound gorges; 

 but it is suggested that the heavy alluvial de- 



posits in the inner valleys were formed while 

 the uplift of the outer range decreased the 

 grade and the activity of the rivers. 



ORIGIN OF THE VALLEY OF THE RHONE. 



The geological changes which have pre- 

 ceded and led up to the existing structure 

 of the vallej^ of the Rhone are traced by 

 Deperet, of Lyons (Apergu sur la structure 

 generale et I'histoire de la formation de la 

 vallee du Rhone, Ann. de Geogr., Paris, iv., 

 1895, 432-452, two maps). The theme is 

 an interesting one, and its treatment ap- 

 pears to be thoroughly competent in a geo- 

 logical sense; but altliough published in the 

 most scientific of French geographical jour- 

 nals under the heading of Geographie region- 

 ale, the essay appears to us to lack the 

 essential qualit}' of geographical matter, 

 inasmuch as the sequence of geological 

 changes in the order of time, and not the 

 development of existing superficial forms, 

 constitutes its chief object. Anything that 

 will throw light on existing forms con- 

 tributes to their recognition and may be 

 properly included under physiographical 

 geography. No collateral study gives more 

 assistance of this kind than geology, from 

 which a knowledge of the structure of a 

 land mass and of the processes at work 

 upon it are derived; but structure and pro- 

 cess must be studied strictly in relation to 

 the forms sculptured by their interaction, 

 if the study is to have a geographical 

 flavor ; and not simply in relation to their 

 order of occurrence, for then the flavor is 

 wholly geological. The first step in the 

 study of form as dependent on structure 

 and process is a thorough knowledge of 

 local geology; this being already acquired 

 and presented for the valley of the Rhone 

 in the above-named essay, we hope that the 

 learned author will now take the next step 

 and describe the regional geography of the 

 valley. W. M. Davis. 



Harvard University. 



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