SUMMARY AND CONCLUSIONS. 119 



CHAPTER VI. 



SUMMARY AND CONCLUSIONS. 



The various groups of geodetic stations have now been con- 

 sidered in detail, and the conclusions, which may be drawn from 

 each, have been indicated, but it is still necessary to review these 

 as a whole and to consider how far they help in the solution of the 

 problems, still in doubt, which were indicated in the opening chapter 

 as those in which the geodetic evidence might help. 



These questions will most conveniently be taken in the reverse 

 order to that adopted in stating them, and it may be said that 

 the geodetic observations fully support the two conjectures, that 

 a rock barrier extends, at no great depth below the surface of the 

 alluvium, from the peninsular rock area to that of the Assam Range 

 to the east, and to the Salt Range to the west. 



We have also found complete confirmation of the geological 

 deduction that the depth of the alluvium along the outer edge of 

 the Himalayas is great, amounting to about 15,000 to 20,000 feet 

 towards the northern boundary of the alluvial plain, figures which 

 are in complete accord with those deduced from the geological 

 examination of the Siwalik hills. 



This agreement, between the results of two wholly independent 

 and different lines of research, leaves little room for doubt that 

 we have reached a correct interpretation of the underground form 

 of the Gangetic trough from near its northern limit to the southern 

 boundary, and that its maximum depth is about 15,000 to 20,000 

 feet, possibly more on some sections, probably less on others, but 

 in most cases lying within the limits named. From this maximum 

 depth, at a distance of from 10 to 30 miles from the northern edge 

 of the plain, the floor slopes upwards, with a fairly uniform slope, 

 to the southern limit, whether this is marked by the reappearance 

 of solid rock, at the northern boundary of the Peninsular area, 

 or by the hidden barriers under the alluvial plains, over which 

 the drainage of the Ganges and Brahmaputra reaches the Bay 

 of Bengal on the one hand, or the rivers of the Punjab flow down 

 to the Indus and so into the Arabian Sea on the other. 



The underground form of the trough in its northern portion, 

 along the edge of the Himalayas, is less clearly defined. On only 



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