46 MEDLICOTTj SHILLONG PLATEA.U. 



soft beds. Similarly in the other example shown in the section to the 

 south of Ryak : if the sandstone at E-yak Lamapara be a repetition of 

 that to the south, as seems to me likely, the slipping- would have found 

 the same encouragement in the soft clays that occur between the sand- 

 stone and the nummulitic limestone. 



8. The Gneiss Sekies. 



On the Shillong plateau, which is orographicaUy a portion of the 

 great Central Asian rock-area, the geologist has to encounter the featm'e 

 which is such a difficulty and disappointment to him all over the rock- 

 area of the peninsula of Hindustan — a total and incalculable stratigraphical 

 hiatus between fresh-looking strata having almost a superficial aspect 

 (however ancient some of them may be) , and great sedimentary formations, 

 both metamorphic and unaltered. Kocks of both these latter types are 

 represented in the Shillong plateau : there is an ancient gneiss, and also 

 a series (largely developed in the Khasia district) , which I will call the 

 Shillong series. I can only speak cursorily of all these rocks j my 

 attention having been directed chiefly to the more recent formations. 



As separately examined, there is a very wide difference between the 

 gneiss and the Shillong series. The latter, over large areas, is only 

 submetamorphic, consisting of schistose clay-slates and granular quartz- 

 ites ; but I cannot say with what precision the boundary between the 

 two series can be laid down, having crossed it only in the low jungle- 

 covered hills on the Assam side, north of Shillong. On the plateau 

 the boundary would pass in a south-south-west direction between 

 Maophlong and Nungklao, a region I haVe not visited; but from 

 descriptions of the rocks about Nungklao, I have little doubt they 

 belong to the older series. The bare massive dome-like features of the 

 Kallong rock may be almost said to be characteristic of the granite or 

 granitoid gneiss of the older metamorphics. Such masses are very 

 common throughout lower Assam. The true granite so largely associ- 

 ated with the Shillong series never makes any approach to this structure. 

 ( 196 ) 



