MKTA.MdlM'HIC LIMKSTONKs TILKKY. 



is present in yellowish -green crystals, which are often idioblastic. with 

 a dominant basal cleavage. It is not infrequently disposed in layers through the rock, 

 associated with <|iiartx and felspar. This is strikingly seen in No. 132, where the felspar 

 is largely microdine. The epidote is always a variety rich in ferric oxide, n 

 indicated by its birefringence and pleochroism. It is only accessonly present in No 

 In Ni>. lit;:! the mineral is undergoing change to a chloritic |>rodnct with anomalous 

 interference tints. 



iii pleochroic plates of blue-green to yellow-green tint is often present 

 in association with the epidote. 



M icnicl/ni'. plagioclase, and quart/, are the colourless silica containing minerals. 

 The potash felspar with ink-recline twinning is closely associated with epidote and 

 quart/. The twinning is, however, not a constant feature, and in the absence oi 

 cleavage and twinning, it is sometimes difficult to discriminate from plagioclase. 



The /tlngiodase present in these rocks is usually of an acid type. It may pos- 

 both pericline and albite twinning lamella?. The felspar of No. 995, for example, is 

 an optically positive type, whose refractive index is greater than that of canada-balsam. 

 but less than that of quartz. It corresponds to albite-oligoclase. Secondary 

 paragonitic (?) flakes are distributed through the grains. In the other rocks the 

 plagioclase very generally shows a refractive index less than that of quartz. The place 

 of the more basic felspars is evidently taken by the abundant epidote. 



<><>artz is quite common as a constituent of the ground mass with calcite. and 

 may sometimes vein the rock as in No. 997. 



In the bands of epidote in No. 132, the associated quartz shows rows of pores 

 along cracks, oriented at right-angles to the long axes of the bands. 



(Jreen lnOtite is present in No. 132, associated with epidote. and a single grain of 

 highly pleochroic 1-mnntdine is also to be observed. 



(7.) (.'ARHOXATK-KRKK CAI.C-SII.H '.\TK HOCKS. 



Two rocks which cannot strictly be defined in the classes already instituted 

 complete the suite of rocks. Both these rocks are completely free from primary 

 carbonate minerals. No. 1153 is a pinkish-white rock with a band of calc-silicate 

 minerals, partlv diopside and partly a dark fibrous amphibole. 



I'nder the microscope, the calc-silicate band shows a very pale tremolitic 

 actinolite. on the outer edge of which colourless diopside is present. This band is 

 Mic.-eeded by a band <>! saussuritic material, in which secondary white mica is plentifully 

 distributed. Quartz is abundant in streaks and lenses. It shows the effect 

 shenrinv stress in the undulose extinction and mortar texture. 



No. l-js is of greater interest. The hand specimen is a greenish -grey rock, in 

 which small porphyroblasts of felspar can be seen. In thin section the constituent 

 minerals are observed to be felspar, epidote, and clinox.oisite MS porpliyroblasts. whilst 



