MKTA.Moltl'lllr U.MKSToNKS TIU.KY. 



ilr is a general constituent in idioblastic prisms, with positive elongaticm. 

 negative sign and large optic axial angle. It is colourless in thin section. l)iit macro- 

 scopirally may develop a pale-green tint indicative of tlie presence of (lie actinolite 

 molecule. 



/'///(/"/*//< is cohtnrless to pale yellow -green, and slightly plrochroir ;md always 

 with a very small optic axial angle. 



Brown hiotilf is |. resent in No. ;}.3,>, and shows peripheral alteration to a light-green 

 chlorite. The phlogopite molecule is probably present in solid solution in its constitution. 

 It is associated with highly refracting and birefringent prisms of rutile. which are of 

 secondary origin, and result from its degradation. The remaining constituents of 

 these rocks call for no special remark. 



(3) DlorslDK-TliKMol.lTK HoCKS. 



Two locks are strictly included within this class. Nos. :><:> and 657. No. <i~. I 

 may be considered here for while tremolite is absent, calcite and diopside are the chief 

 oonstituentB. 



No. :{n:{ is a coarse-grained grey rock with large crystals of diopside measuring 

 up to 1 inch or more in length. It is associated with light-green fibrous amphibole. 

 I 'ink-coloured calcite is sparsely distributed, and quartz can also be recognised macro- 

 scopically. 



NO. (i.")7 is a finer grained rock in which on weathered surfaces, the new-formed 

 silicates project. As such, can be recognised biotite. mica and green diopside. 



No. <).">! is a flesh-coloured crystalline marble containing porphyroblasts of light- 

 green diopside. 



The constituent minerals of these rocks are m/r/'/r. ilio/isidt'. lirnntlil,-. actinnlitc. 

 luntiti'. i>ltH/iiH-ltiNr. Ilium!,'. \i n-<>,>. itfHiiiic. and secondary white mint. Dolomite has not 

 been recognised in thin sections by the 1 winning, nor in those sections examined by 

 staining. In No. 651 all carbonate can be decomposed in dilute hydrochloric acid. 



The colourless />i/r<>irtn' <>| No. :{o:{ shows a lamellar twinning, and parting planes 

 parallel to the 001 and 100 faces. The extinction angle / A c is 41. In No. 657 the 

 pvroxene is a colon rles.-, to pale green type. The colourless fri'imilitc of No. :5<>:! i> 

 fibrous parallel to the c axis and is wedged between larger crystals of diopside. The 

 amphibole of No. 657 is distinctly coloured and pleochroic in light-green tints. Tremolite 

 in this KM k is also a constituent of pseudomorphous assemblages of white mica and 

 xoisite. which in some cases can be shown to take the place of plagioclase felspar. 



I'luf/iiii-lns, is developed in rounded grains, sometime^ .\itli twinning lamella' 

 after the albite and pericline laws. The more b;isic types are the less stable, giving 

 rise to pseiidomorphs in which mica and x.oisite are important constituents. There 

 are rounded grains whose refractive index approximates to that of canada-balsam. 

 and appear to be near oligocla>e in composition. 



