14 WIDDLEMISS: THE GEOLOGI OF [DAB STATE. 



One is impressed by the wide expanse of this formation, whose 

 flowing slopes and steadily winding strikes with a moderate folia- 

 tion dip. seem to imply great thicknesses (amounting to thousands 

 of feet) of a rock-type singularly uniform as a whole, though not 

 in detail. It is only when the collections from the various parts 

 have been subjected to microscopical examination that differences 

 appear. These are best exemplified in the areas where quarries 

 and railway cuttings have assisted in the work of exposure. Hence 

 the majority of the penological types whose descriptions follow 

 are from the neighbourhood of Vadali or Khed Brahma, but it is 

 believed that those types may be taken as thoroughly illustrative 

 of the whole of the calc-gneiss areas. 



Under the microscope a specimen of the more ealeiferous variety 

 from the quarries on the railway 11 miles 



Microscopic details. ,, r ., , ,. .> -. ,1 , jt __«;«, ,> np f 



1 north of \ adali {ffiY shows the mam part 



of the slide (12130) 2 to be crystalline grains of ealcite of rather large 

 size. These were proved by Lcmberg's staining method to be all 

 ealcite without any dolomite. Along with them is a considerable 

 amount of almost colourless pyroxene in irregularly rounded smaller 

 grains clustered together. The variety of pyroxene here present 

 (it may parenthetically be remarked) is peculiarly characteristic 

 of this geological region, and we shall find it giving the dominant 

 note to a. number of rock-types of the State. In this particular 

 group of calc-gneisses it appears to the eye in hand-specimens 

 as little blebs, or groups of blebs, without crystal faces, and of a 

 colour varying from pale to dark grey or greenish grey or 

 to a brighter bluish green, becoming very pale tints of the same 

 in thin section. Tn the specimen just quoted its general appearance 

 together with its high index of refraction, rather strong double 

 refraction, absence of pleochroism and its type of cleavage are 

 easilv presumptive of pyroxene. The lack of definite crystal out- 

 lines makes the determination of its other optical constants rather 

 uncertain, but in numerous related specimens some of the sections, 

 which present a single well-developed set of cleavage traces parallel 

 to the long axis of the grains, may be presumed to be in the 

 prism zone, and the extinctions here with reference to the axis 

 of lesser elasticity (Z A c) reach values of from 38° to 44° which 

 are sufficiently characteristic of the diopside class of non-aluminous 



1 Number in Q.S.L register of rock specimens. 



2 Numl er in C.S.I, register of miorOBQO] e slides 



