^"'^-* 57-] ^^ SOTJTH-CENTRA.L CEYLON. 205 



J 



is crowded with green malacolites. At the junction exists a 

 line of dark minerals. Under the microscope the ' Band " is re- 



esented by a fine-grained aggregate of calcite and malacolite, 

 tiie latter preponderating, the former interstitial. The smaller 

 grains of malacolite are full of inclusions, perhaps of a carbonate. 

 The limestone consists of plates of dolomitic calcite,^ and is excep- 

 tionally rich in malacolite, thus resembling the rock on the other 

 side of the junction, except that the carbonates predominate over the 

 malacolite, and the whole is coarser. The last-named mineral 

 becomes more plentiful as we approach the boundary, and is also 

 serpentinized along cracks and edges ; while near the junction 

 many grains are converted into yellow and green serpentine. The 

 line of demarcation between the two rocks consists of greenish and 

 yellow serpentine, without definite form and showing but few traces 

 of its origin from malacolite. 



A second contact-section, cut from another specimen a couple of 

 yards or so away, unfortunately gives but little information about 

 the composition of the ' Band ' near the junction. We find the same 

 serpentinized zone ; and the line of demarcation between the two 

 rocks is not strongly marked, so that it is difficult to say where 

 one begins and the other ends. This section is, however, note- 

 worthy for the grains of spinel embedded in the serpentine-zone. 

 There is some iron-oxide, possibly of the nature of a residue, and 

 a few small flakes of reddish-brown mica, almost colourless for 

 ^-ibrations normal to the basal plane. The spinel is of a dull 

 sage-green, considerably cracked, and occurs in rounded subanguiar 

 grains up to '025 inch in diameter. 



Perhaps some monticellite may be present, as well as malacolite. 

 The hmestone 12 inches from the junction contains abundant grains 

 of malacolite, fresh and not serpentinized, and a few plates of 

 slightly-coloured augite. The dolomitic calcite here and in the 

 cuttings to the south often has a vermicnlated structure, owing to 

 the presence of threads of a colourless mineral with an exceedingly 

 low index of refraction and apparently no action on polarized' 

 light." Yery rarely we find a few flakes of yellow-brown mica, and 

 still less frequently a grain of spinel. Prisms of pale blue apatite 

 are common, ranging up to '07 inch in length. When detached 

 entirely from the rock and examined in polarized light we find them' 

 to be strongly dichroic (pale blue to pale claret-red).'^ 



A specimen of the ' Band ' distinguished by the presence of large 

 brown plates of mica, 1 to 1| inches across, deserves a few words. 

 The rock is much lighter in colour than normal specimens. A 

 thin section shows that tliere are three primary minerals and one 



^ The rock eflfervesces sharply with cold hydrochloric acid. See Bull. Soc. 

 Mill. France, vol. xii (1889) p, 336, wher^e the presence of both calcite and 

 dolomite are recorded by M. Lacroix. 



- An identical structure is described and figured by M. Lacroix in the dolomite 

 of these rocks ; see Bull. Soc. Min. France, vol. xii ( 1889) pp. 337-38 & fig. 60. 



^ See A. K. Coomara-Swamj, Quart. Journ. Geol. Soc. vol. Ivi (1900) p. 6(X) ; 

 Lacroix, Bull. Soc. Miu. France, vol. xii (1889) p. 339 ; and C. Barrington Brown 

 ifc J. W. Judd, Phil. Trans. Roy. Soc. vol. clxxxvii (1896) A, p. 212. 



