56 MEDLICOTTj SHILLONG PLATEAU. 



The absence of local intrusive phenomena in connection with the 

 great granite masses is the more surprising when we come to observe in 

 the southern region the frequency of such special intrusions of a similar 

 granite. These are not either always in the form of dykes ; there are 

 miniature protrusions on the pattern of the large masses. Such features 

 are more common than would appear at first. It is only possible to 

 observe along the paths ; and these are almost always made on spurs 

 or by ladders down cliffs, formed of the harder quartzose strata ; owing to 

 the more ready disintegration of the granite,, it is generally impossible 

 to find in place the rock of which huge blocks are found abundantly in 

 the torrent bed, and which must be derived from some outcrop within, a 

 short distance up the enclosed gorge. The best instances of these in- 

 trusions that came under my observation are on the east side of the valley 

 of the Theria river, near the boundary of the Silhet trap : at the village 

 of Turingai there is a good sized boss of coarse granite ; and in a little 

 valley a quarter of a mile to south of the village there is a twQ-foot 

 dyke of the same rock cutting across a mass of quartzite. 



The relative age of the trap and the granite is a point of some interest | 

 and my observations go to prove that the granite is the younger of the 

 two. I only in one spot found the Khasia greenstone in close contiguity 

 with the granitic masses. This occurs at the point south of Maoreng, 

 where the boundary of the Molim granite takes its sharpest turn ; and 

 again in the stream half a mile to south-east of this bend. The 

 actual contact is not exposed; but both rocks are in place and ap- 

 parently quite normal within five yards of each other. Thus the trap 

 forms no exception to the neutral relation of this granite to the rocks 

 along its boundary. I have never seen any trace of the greenstone penetra- 

 ting the granite ; but in the bed of the torrent below Surarim on the 

 east there are several clear sections of small dykes of granite ramifying 

 through the trappean rock. The general direction of these dykes is 

 with the strike of the quartzites, which is here parallel to the boundary 

 ( 206 ) 



