SOILS OF THE ARID AND HUMID REGIONS. 



413 



The Brahmaputra Alluvium in Assam. Aside from the 

 immediate alluvium of the Indus, of which no definite data are 

 available, the Indo-Gangetic plain represents the drainage of 

 the southern slope of the Himalaya chain. That of most of 

 the northern slope is represented by the Brahmaputra, which 

 not only orginates in a region of heavy precipitation Thibet 

 but continues in the same throughout its course, and rounding 

 the easternmost spur of the Himalaya range enters, in southern 

 Assam, upon the region of the maximum rainfall known. Its 

 alluvial deposits should therefore show the reverse character- 

 istics of those of the Ganges; they should, as thoroughly 

 leached soils, be poor in lime, magnesia and potash. We have 

 fortunately on this subject the excellent work clone by Mr. 

 H. H. Mann for the Indian Tea Association, the report of 

 which was published in 1901, and contains, besides a large 

 number of analyses, good descriptions of the general soil and 

 cultural conditions of the Assam tea districts, with suggestions 

 for their improvement. 



The tea plantations of Assam are located almost wholly on 

 the new and old alluvium of the Brahmaputra river, bordered 

 on the north by the eastern spur of the Himalayas, on the 

 south by the low ranges of the Khasia hills. The soil is mostly 

 quite sandy, the late alluvium gray in color, the older reddish 

 and more loamy. Of the four analyses given in thetable and 

 fairly representing the average character of these soils, the two 

 first are from the north side, the latter two from the south side 

 of the river. 



It will be noted that the prominent feature of all these soils 

 is an extremely low percentage of lime, the general average 

 being about .08% as against nearly 1.0% in the average 

 Indo-Gangetic soils. In the latter, potash ranges between .65 

 and ./o^r ; in the Assam soils between .25 and .35. Magnesia 

 averages nearly 1.3 in the Indo-Gangetic, against about .50 in 

 the Assam tea soils. It is thus apparent that the same general 

 facts as regards the leaching-out of soil ingredients already 

 shown for eastern and western North America are strikingly 

 verified in northern India ; but reversed as regards the points 

 of the compass. The preferential leaching-out of lime as com- 

 pared with magnesia and potash, is here again well exemplified. 

 It would be interesting to have an analysis of the Brahma- 



