W. F. Sume — Notes on Russian Geology. 555 



Seas which are so abundant in S.E, Russia. (I have sometimes 

 wondered whether such an extension might be the result of the 

 elevation of the sea-level due to the nearer presence of an ice-sheet, 

 such as has been suggested, if I mistake not, by the Rev. 0. 

 Fisher, Dr. Croll, and others.) 



A far more important suggestion was that made by Sir C. Lyell 

 for the Rhine sandy clays (Principles of Geology, chap. xvi.). The 

 origin of the materials is attributed to glacial action during the 

 ice-period, and he accounts for the homogeneity of the materials 

 as being due to the same cause. The Loess itself is in reality a 

 flumatile silt deposited in the lower reaches of the river by the 

 action of floods. To account for its enormous extent, and consider- 

 able elevation, Sir C. Lyell called in the aid of numerous elevations 

 and depressions, although assigning no particular reason for such 

 important earth-changes. 



Prof. Heer (Urwelt der Schweiz. p. 521) held that Loess was 

 sand and mud deposited from glacial torrents. 



Mr. Belt, in the work above mentioned, and in numerous others 

 dealing with various parts of the globe, regarded the materials as 

 being- due to the floodino; which would result if an ice-sheet blocked 

 up the mouths of the rivers and occupied the marine basms. I 

 do not know what grounds there are for believing such a formidable 

 advance of ice to have taken place, and although such a great lake 

 lying between the ice-sheet and the southern mountain barrier may 

 explain a few features, the vertical irregularities, the great abundance 

 of land-shells, and the want of stratification still remained as great 

 a mystery as ever. Agassiz (Jahrbuch fiir Mineralogie, 1867, pp. 

 676-680), lent his powerful support to the lake deposition view. 



It was not, however, until the appearance of Baron von Richthofen's, 

 "China," Vol. L (see chap, v.) that the great forward step was taken 

 in the discussion of the subject, and an explanation was given which 

 satisfied a large number of then existing difficulties. One important 

 factor, the loind, had till then been entirely overlooked, and was now 

 at one bound to explain the formation of some of the most prominent 

 deposits met with on the surface of the earth. But if I under- 

 stand him aright. Baron von Richthofen demands certain physical 

 conditions, which shall be favourable to Loess formation. They are : 

 1st. An area, which shall be almost entirely unconnected with the 

 main drainage, to use his own words, an " abflussloses Becken." 



2nd. Thus deprived of any means of outlet, the water and its 

 contained salts would settle in the hollows giving rise to salt lakes, 

 which finally by evaporation would become salt steppes. These 

 dry lake-bottoms thus exposed are subjected to subaerial action 

 alone, wind being especially active in the redistribution of the 

 component particles. Loess may also be formed directly by the 

 denuding power of wind action alone, quite independently of the 

 above physical conditions. 



In the first case, as soon as an exit was provided, denudation 

 began. The salts, previously collected in the soil, are leached out, 

 and the once barren Steppe becomes a fruitful plain, and the 



