Western Australia. 151 



The felspars are also more turbid, and in them epidote is not so 

 prevalent. Leucoxene is rare. 



12370 is a rock of the soft green type. 



Minei-als observed : chlorite, quartz, calcite, felspar, magnetite, 

 apatite, epidote. 



Long, thin columnar crystals of felspar, partially or wholly altered 

 to carbonate and green chlorite, with usually a green bonier of 

 chloritic scales all I'ound the crystals, are the most prominent feature 

 of the slide. The felspar appears to be andesine. Between these 

 forms are clear areas of quartz with chlorite inclusions; some of the 

 quartz appears originally interstitial, but most is doubtless secondary. 

 There are numerous apparent intergrowths of calcite or chlorite and 

 quartz forming a micropegmatite, and though the calcite and chlorite 

 may be due to decomposition of felspar the structure in this case 

 is more probably of secondary origin. On the other hand, a few small 

 areas of micropegmatite in which the felspar is only kaolinized are 

 regarded as original. There are a few needles of apatite, numerous 

 grains of magnetite, and some small plates of epidote. 



Though the alterations to which this specimen and 12324 have 

 been subjected are quite different, the structure of the rocks is some- 

 what similar. There is even in 12370 a suggestion of ophitic 

 structure. The rock is of doubtful origin, but is classed as originally 

 a quartz dolerite. 



12377 and 12379 are of very similar type to the preceding, but 

 though they are undoubtedly originally the same rock their structure 

 is more indefinite. 12377, in particular, approaches 12322 in 

 structure, and it would seem that the difl'erence between the 

 two is due only to a difference in the type of alteration each 

 has undergone. 



2108 is more closely grained and has a larger amount of chlox-itic 

 scales, 'i'he felspar columns are very large, and the mineral is now 

 represented largely by calcite, chlorite, and epidote, but in places by 

 quHrtz and chlorite, or quartz and calcite. 



In 12378 there has been a much more complete mineral and 

 structural alteration. There are few signs of idiomorphic felspars: 

 the structure is distinctly granular, and the slide consists of a mixture 

 of chlorite, calcite, quartz, epidote, and iron-ore. Yellowish epidote 

 is pai'ticularly abundant in smnll platy iiggregates. In part of the 

 section the constituents are arranged parallel, as if the rock had been 

 sheared since its decomposition. One large columnar crystal with 

 perfect longitudinal cleavage, straight extinction, very low bire- 

 fringence, and a biaxial figure has been referred to zoisite. 



12310 is a dark-green carbonated chloritic rock. Under the 

 microscope, it appears at first sight to consist of a basis of almost 

 isotropic chlorite in which are grains and crystals of a carbonate, small 

 plates and grains of nearly colourless epidote, and some dark-grey or 

 brown areas with the appearance of leucoxene. Closer study, 

 however, shows that the chloritic basis contains remains of small 

 columnar, almost lath-shaped crystals of twinned felspar. Siiu^e tliere 

 appear to be no idiomorphs of any size the whole rock seems to be 

 composed chiefly of the laths, and the suspicion arises that it is but 



