134 klDt)LEMISS: Till'. (JKOU)GY OF 1DAR STATU. 



specimens Nos. ^ and f^—^ 5 (12502 to 12511). They also pene- 

 trate the white pyroxene of that area. All are too much altered to be 

 worth attempting to describe in any detail ; but long blades of 

 plagioclase, and probably remnants of pyroxene and amphibole 

 and even olivine, can often be recognised with some difficulty. 

 Some of these venis are 2 to 3 feet thick. 



In his account of the basic dykes of Western Rajputana, 

 . x . Mr. LaTouche (he. cit. p. 91) includes a de- 



( orrelation. .... 



scnption by Sir T. Holland of a rock very 

 similar to those described by me above, namely that forming the 

 ordinary dykes of that part of Rajputana. such as the large dyke 

 south of Jalor ^* 5 which cut the rhyolites and granites. The 

 description is that of an olivine dolerite with biotite, agreeing so 

 remarkably with my Khed Brahma and Kawa rocks that it is 

 evident that besides the acid igneous rocks there is a further link- 

 connecting together also the igneous basic rocks of the two areas. 

 The rarer tinguaite, described by Holland on the next page 

 of LaTouche's memoir, has not, however, been identified in the 

 Idar region. 



KAWA HYBRID ROCK. 



The Kawa basic dyke, besides being intrusive among the calc- 

 gneiss, also penetrates, as already stated, the 



dvko'^'nLrta!;^-" * nmite .° f War W * thp 8 ™ fch ™* & the 



little hill near Kawa village. In doing so 

 the two rocks have become closely associated one with the other, 

 producing along the zone of contact a rock of an abnormal com- 

 posite character, which I am disposed to regard as of the nature of 

 those which Mr. Harker has described as " hybrid " rocks. 1 



The section exposed at the south face of the Kawa hill is as 



r . ,, ,. follows: to the west the basic rock— A\, 



Field section. „ ,- "-4(13' 



4 6 4— already described, forms the main mass of 

 the crest of the ridge running away to the north. To the east, 

 and forming a little knoll at the south-east extremity of the ridge, 

 normal Idar porphyritic granite is exposed. But coming between 

 the two along a N.N.E. — S.S.W. line, there is a band, roughly 

 some 50 feet wide, consisting of the composite or hybrid rock 

 o ? 6 5 9 (12514), rather intimately veined by the basic dyke and under- 



1 " Natural History of Igneous Rocks " 1 909, p. 340 tl spq. ; also " Tertiary Igneous 

 Rocks of Skye" Mem., G. 8. of Scotland, 1004, and Canock Fell, Q. J. G. S., Vol LJ 

 1895, etc. 



