124 MXDDLEMISS: THE CJKOLOGY OF IDAR STATE. 



Accessories, as iron ores, and apatite, zircon, etc., are sparingly 

 present, and are frequently included in the biotite as just mentioned. 



This variety of the granite, as indeed many of the varieties 

 often contains dark, fine-grained patches 

 Baeio cognate xcno- (cognate xen oliths of Harker). No. / 3 5 (J 

 (12450, PI. 14. fig. 2) is such a rather fine- 

 grained xenolith enclosed within 4 2 ;i :> 8 from near Laloda. This 

 fine-o-rained inclusion contains a fair amount of quartz, microeline, 

 plagioclase. and biotite having dark, green and yellow pleochroism. 



Fine-grained micro-granites and granophyres are fairly well re- 

 presented by many specimens, such as 3 2 ( ; \ 

 Micro-granites a.ul (12462) from Satharva or Govandi, r> 2 ^ 

 granophyres. (12464) from Hamirgad and *& (12465) from 



Jamla. Most contain, in rather scattered distribution, phenocrysts 

 of microeline, orthoclase, quartz and biotite set in a micro- 

 granitic or o-ranophvric ground-mass. Many also show basic cognate 

 xenoliths (as do the normal granites) containing much biotite, 

 some small white garnets (?) and quartz grains, e.g., £fo (12465). 

 The Jamla rock. 4 2 / 9 suggests a passage over into the coarser 

 varieties of the quartz-porphyries, not only petrologically and 

 texturally, but also by its geographical position in the immediate 

 neighbourhood of a group of typical quartz-porphyry hills. 



Among the micro-granites, fjfc (12163. PL 11, fig. 3), from 1 mile 

 north of Wantra, is somewhat exceptional. This rock is very dark and 

 fine-grained, with sparing, widely distributed phenocrysts. It is 

 the heaviest of any of the Idar granitic rocks, the specific gravity 

 being 2-767. In the fine-grained ground-mass of microeline, plagio- 

 clase and quartz, the rare, large porphyritic felspars occur and also 

 large numbers of moderately large, ragged plates of biotite of the 

 usual type, together with similar groups of grannies of pale green 

 diopside changing into uralitic hornblende. The diopside, is some- 

 times intergrown with the biotite. 



Good examples of granophyrie structure in the gronnd-mass are 

 exhibited by 4 2 3 5 j , (12468), from 1 mile W.S.W. of Kesarpur (Jamla 

 neighbourhood). This rock is characterised by orthoclase with 

 Carlsbad twins, and not microeline. The micrographic quartz and 

 felspar frequently surrounds the orthoclase grains with mutual 

 optical continuity. In other cases quartz grains similarly form 

 nuclei for a similar optical orientation of the micrographic inter- 

 growth. 5 2 - (12464, PI. 14, fig. 4), from north of Hamirgad and west of 



