68 IUDDLEMISS: THE GEOLOGY OF IDAE STATE. 



north of Jesangpur — the last exposure being only poorly seen in 

 the shallow stream-beds of that part. These several widely 

 separated partial outcrops roughly follow a line stretching N. — S. 

 between Bolundra and Abharpur, a distance of about 10 miles. 

 Owing to alluvium it is not certain whether all represent the same 

 or different beds. 



In the better exposures, as seen W.S.W. and S.S.W. of Baman- 

 vada, the prominent white pyroxene occur- 

 Wliite pyroxene : di- rences indicate beds of the mineral of from 2 

 to 3 feet thick, totalling 8 feet in one section 

 and 30 feet in another, associated with two or three beds of about 

 an equal amount of calcite and calcite-tremolite rock, etc. The 

 pyroxene beds are very coarse to medium-grained, and consist of almost 

 pure pyroxene— specimens Nos. 8 * 4 « 3 — 8 »& (12374— 12379, PI. 11, fig. 5). 

 Its white, creamy white, or pale whitey-grey colour at first suggests 

 a coarse felspathic pegmatite. Its true nature as a pyroxene, 

 however, became evident on examination of the more or less com- 

 plete crystals and cleavage fragments broken out of the rock. The 

 specific gravity of these was determined as 3*10, the hardness as 

 5 — g } an d the mineral was practically infusible, except on the edges 

 of thin chips. Chemically examined in the Geological Survey 

 laboratory by my colleague Mr. Tipper, it was found to be slightly 

 aluminous with a little iron, and with calcium and magnesium in 

 very fair quantities. The mineral, therefore, must be principally 

 a calcium-magnesium silicate. From thin sections cut in typical 

 directions it shows the single and double refraction of pyroxene, 

 an interrupted prismatic cleavage angle of 86°, a more perfect 

 orthopinacoidal cleavage, and distinct basal cleavage or parting, 

 the two latter making an angle of 74° with each other. The extinc- 

 tion angle Z A & is 38°— 39 ; it is optically positive. All these data 

 plainly indicate a pyroxene of the diopside group. Along with 

 the large crystalline grains there is a very little interstitial quartz 

 and calcite, the latter also appearing along cracks as a decomposi- 

 tion product, and being sufficient to give a fugitive effervescence 

 with acid on freshly broken surfaces (y 2 ^, 12380). There is also 

 a very little sphene. 



The purer bands of this diopside rock show nothing but this 



one mineral, except the change in a few places 

 Change to amphibolc. . . ,. , . , 



oi the pyroxene to tremolite or pale greenish 



actinolite. In specimen No. g ? 4 fi 9 (12381) the process of the replace- 



