KHASI HILLS. 157 



the small intermediate glen, are throughout of a very constant litholoo-i- 

 cal character. They are all a basaltiform greenstone, dense and close-grain- 

 ed, with very few and small vesicles, or air bubbles. 

 General character. .. . . . 



The rock divides into prismatic masses, assumin tr 



in places a semi-columnar aspect ; but this structure is not well developed. 

 Where long exposed it decomposes on the surface ioto a ferruginous 

 ochrey sand. Near the junction with the overlying sandstones this 

 greenstone is traversed by numerous small veins of quartz which fill all 

 the cracks and fissures in the mass. These do not occur at any distance 

 from thp sandstone, and appear to be the result of the subsequent filliafT 

 in of small cracks by silica derived from the overlying sihceous rocks. 

 This is the general character of the rock throughout the large area 

 over which it is exposed. 



North-East of iilow-phlang greenstone occurs, not in the form of a 

 great underlying sheet of rock supporting the 

 sandstones, but as a dyke or wall of this io-neous 

 rock, cutting through the beds of the mechanical series. Here the 

 character of the rock is somewhat different ; instead of the basaltiform 

 structure and composition, which prevail iu the mass, it is diallaoic 

 more largely crystalline, and is a true diallagic greenstone. I am dis- 

 posed to view it, however, notwithstanding this difference in aspect, as 

 connected v/ith, and probably an off-shoot of, the great mass of greenstone 

 to the South. 



Other dykes occur in the district South of the village of Laikro, which 

 have, though in a much smaller degree, the same mineral aspect. 



All these dykes have a common direction, namely, they all head 

 or strike nearly due North-East, coinciding with 



Direction of dykes. _ 



the main or general direction of the great river 

 valleys in which the greenstone is so well exposed, (a) 



(a) The road from Cherra Poonjee to Gowahatty in Assam passes for several miles 

 over this greenstone between the valley of the Kala-pani and that of the Boga-pani. This 



