202 MR. J. PARKINSON ON THE GEOLOGY [^^^.V 190^' 



lighter bands the only ferromagnesian mineral is a mica ; the 

 remainder consists of grains of quariz, plagioclase, and some 

 orthoclase. The extinction of the plagioclase symmetrically with 

 regard to the trace of the composition-plane varies from 7° to 9°. 

 The darker parts of the slide are distinguished by large plates of 

 green hornblende and a quantity of brown mica. The two minerals 

 are intimately connected the one with the other ; in one instance 

 the mica seems to be an alteration-product of the hornblende. The 

 constituent grains of the light and dark parts interlock, and there 

 is nothing approaching to a sliarply-defined line of contact. Quartz 

 is less plentiful in the darker parts ; a few grains of an apatite- 

 like mineral occur, and an occasional crystal of zircon. There is 

 very little quartz vermicule, but no microperthite. 



In the cutting just below Kadugannawa (that is, on the west) the 

 banded rock becomes strikingly garnetiferous. The garnets favour 

 the dark parts in their distribution, but occur also in the lighter. 

 One or two are of the size of a very small pea, but this is exceptional. 

 A typical specimen is dark and micaceous, markedly foliated, slabby 

 in fracture, and crowded with small garnets, about '025 inch in 

 diameter. A thin section shows that hornblende is entirely absent, 

 its place being taken by the garnets. These are irregular in 

 shape, rather cracked, and may be either pyrope or almandine.' 

 Occasionally we find mica-flakes embedded in the garnet. The 

 plagioclase gives symmetrical extinctions from 18° — 18° to 22°-- 22°. 



A thin section has been cut from a specimen taken near the 

 small wayside station of Balana, on the Colombo side of Kadugan- 

 nawa. Here the darker rock is in excess, but the white bands are 

 still clearly seen in places. Under the microscope we see it to be 

 closely related to the series already described. It contains a 

 considerable quantity of hornblende and mica in approximately 

 €qual proportions. 



A thin section has been cut from a very similar rock cropping 

 out on the path to Lanka Telika, near Kandy. It is a black 

 and white speckled rock, the white constituents being granular and 

 saccharoidal. Under the microscope the resemblance to the Balana 

 rock is very great : the ferromagnesian silicates are somewhat less 

 strongly developed, but iron-ores are not uncommon. 



(c) Railway to the north of Mahaiyawa (Kandy). — A 

 well-preserved banded rock is found to the north of Mahaiyawa. 

 It sometimes contains quartz-grains of considerable size and, locally, 

 garnet. Not far from this is a small quarry near the railway, exca- 

 vated in a grey biotite-gneiss, streaked rather regularly by a red 

 coarse granite, which occasionally contains large black mica-plates. 

 The rock is often very coarse, and exhibits big eye-shaped felspars 

 such as were seen near Eambukkana. The bands w^hich this srranitc 



fci^ 



^ M. Lacroix refers the garnet to almandine, Bull. Soe. Min. France, vol. xii 

 (1889) pp. 288, 306, etc. 



