THE GEOLOGY OF WOIiLl HILL. 



589 



calcite in the fissures of the rock. The pjTites and the calcite seem to be 

 coeval as the crystals of pyrites are very often covered over by crj'stals of 

 calcite. The pyrites does not occur in the traps, but is common in the 

 chertif.ed fresh water beds of Sewri in fairly big amorphous lumps. It also 

 occurs in the aqueous deposits at Bhoiwada. 



II. The mos^jidely dissemmated mmeral in these sedimentary beds is 

 undoubtedly calcfw. Besides impregnatmg the mass of the rock it is exten- 

 sively found deposited in a crystalline form in the cracks of the beds and in 

 the cavities in the lower trap generally in association with crystalline quartz 

 and zeolites. It is rarely intercalated with the shales. It occurs in a variety 

 of pretty forms mixed up together on the same specimen. In colour it varies 

 from black, dark brown through cream to piu-e white. In general it is 

 translucent or opaque, but small bits can be obtained perfectly transparent. 

 The crystals are invariably well formed and regular but rather of a small size 

 and the aid of a magnifying glass is necessary to bring out their full beauty. 

 Striations on the fractured surfaces or on the natural faces of the crystals 

 are common. Sometimes the siu-face is dull and wavy as if the crystals had 

 cooled out from a molten material. Smaller crystals of the same or dific; 

 ent kind are very often partially embedded in the larger ones or are found as 

 excretions on the exposed surfaces. 



it will be noticed that most of the specimens are small in size. This is due 

 to the fact* that the deposits, though extensive, are occurring at right angles 

 to the sedimentary layers, and any attempt to detach the mineral results in 

 splitting the layers and with them the mineral. The following are the chief 

 varieties in which the calcite occurs though a more careful investigation may 

 disclose new forms or may reduce those described here to a few primitive 

 types. 



(a) Calc-spar is the commonest form of calcite. It occurs in fairly big lumps 

 and in all shades of colour, from dark brown to milky white. Unlike the calc- 

 spar found in trap rocks, the lumps in the sedimentary beds show a tendency to 

 crystallise out on the surface into other forms, in fact the mass appears to 

 be a random mixture of a variety of crystals. 



(6) Next the calcite shows in independent rhombic crystals with angles 

 sometimes approaching very near to right angles, givmg to the crystals the 

 appearance of cubes. Very often it is only a corner that projects beyond the 

 mass of the mineral and the crystal stands out as a three-sided pyramid. Ihe 

 colour is sometimes waxy greenish. Twins are quite common. 



(c) Calcite is also found deposited as flat oblong discs with facetted sides. 

 The top and bottom are plain. The crystals are found lumped together and 

 are partly transparent and partly translucent. In some cases the edges or 

 the top layer is opaque and pearly. These crystals probably pass mto the 

 barrel shaped ones by a considerable mcrease m theu: thickness. 



(d) Crystals resembhng dog tooth spar occur in fine six-sided do"We pyra- 

 mids joined at their bases. The height ^^ ^1^%?^^^^ ^ ^%"1T .T '^'d 

 double the width of the base, but very often the ratio between the height and 

 the base is considerably less and the crystal resembles ^'^''y^ J"^;^.'^^/ J^ 

 sided quartz crystal. Frequently only one Py^^^^lVr^rf u^iito The 

 general mass of the mineral. The colour is in general translucent wlnto. iiio 

 fr'stat "rerally end in sharp points but the top sometime, erniuja^^^^^ 

 three quadrilateral faces meeting in a three-sided pyramid. Some of the faces 

 often stop short of the apex. ., , , i. „..„„ 



