30 MEDLICOTTj SHILLONG -pLATEAV. 



The great secondary trap formation whicli underlies the cretaceous series 

 to the east does not appear here at all^ though it may be presumed to 

 underlie at no great distance ; and the lower rocks in contact with the 

 cretaceous seem to belong to the older gneiss, not to the newer metamor- 

 phics of the Shillong series, or to the granite associated with this series. 

 There is but one group of cretaceous strata here; some 500 to 600 

 feet of strong-bedded, coarsish, pale yellowish sandstones with subor- 

 dinate carbonaceous shales and coal. The upper beds of the Cherra 

 section do not seem to be represented. These newer sedimentaries rest 

 against, rather than upon, the crystallines ; and they have imdergone a 

 considerable amount of contortion, as appears to be always more or less 

 the case in the strata at the base of the high plateau. The nature of the 

 disturbance of the strata seems still to indicate considerable relative 

 displacement of level — either the elevation of the metamorphic area or 

 the depression of the newer rocks, or both. This has not taken place 

 by a fault along the surface of junction, nor yet by so regular a 

 semi-anticlinal bend as in Silhet. The plane of contact is well seen 

 in the bank of the Sumdsari just north of Seju ; it underlies at 80° to 

 the south-south-west, but it is thus parallel to the dip of the sandstone, 

 and the bed next the gneiss is a true bottom bed containing blocks of the 

 crystalliaes against which it rests in its original relative position. . The 

 surface of the crystallines seems to have bent up or down with the 

 sandstones. 



In the region of the Kalu river, at the west extremity of .the 

 hills, the only cretaceous rocks seen are exactly of the same description 

 as those on the Sumesari ; the only difference being that they have 

 undergone scarcely any disturbance of contortion; the sandstones are 

 seen lapping up over a steep surface of the gneiss on the flanks of Tiira 

 and Harigaon Hills. In the lower hills touching the Bramahputra at 

 Singmari, the gneiss weathers out here and there from under a covering 

 of the sandstones ; still this gneiss only occurs on the prolongation of 



( 180 ) ' 



