tHE UNDERGROUND FORM OF FLOOR OF GANGETIC TROUGH. 71 



deflections lies at about 70 miles from the main boundary, a some- 

 what greater distance out from the edge of the hills than in the 

 series just dealt with. The southerly deflections at the stations 

 further south are smaller in amount than further east, but it must 

 be borne in mind that this series of stations lies not far from where 

 the general course of the boundary of the alluvium runs about 

 north-north-west ; the deflections due to the trough would, there- 

 fore, be more nearly east and west than north and south and the 

 component in the meridian, which is that measured by latitude 

 observations, is necessarily reduced in amount. Still further south 

 larger deflections come in, but here the effect is partly, and 

 probably mainly, due to the southerly deflections in this part of 

 the peninsular area, with which we are not here concerned. 



The western series exhibits some peculiarities which it is not 

 easy to explain, though they are doubtless connected with the 

 narrowing of the alluvial area on the continuation of the line of the 

 Aravalli hills. The northerly deflection is maintained for a dis- 

 tance of a hundred miles from the main boundary, and only beyond 

 this distance does a small southerly deflection come in at a couple 

 of the stations in the alluvium. Then, we have the northerly 

 deflections at Agra, and further south the southerly deflections 

 of the northern peninsular area. It is evident that on this section 

 there are other influences at work counteracting the effect of 

 the trough ; or, in other words, that the trough is of smaller dimen- 

 sions than further east, and no longer has that preponderating 

 effect which was there met with, and it is noteworthy that the 

 stations of Datairi and Bostan, where the northerly deflections 

 show that there is no regular shallowing of the alluvium in a 

 southerly direction, or that it is insignificant in amount, are situ- 

 ated on the direct continuation of the line of the main range of 

 the Aravallis, which may reasonably be expected to continue 

 under the alluvium with much the same surface contour as they 

 show further south. 



A third series of latitude stations is situated near the 85° meri- 

 dian but does not extend across the alluvium, and in its southern 

 portion is affected by some local cause leading to abnormal deflec- 

 tions. In spite of these drawbacks the series gives some infor- 

 mation and needs notice. A list of the stations is given in table 

 No. 21 ranged in order of distance from the outer edge of the 



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