GEOLOGY. 



The Ranchi and Hazaribagh districts are occupied 

 especially by the metainorphic rocks. Granitoid Gneiss, 

 mostly Hornblende gneiss, * is one of the commonest. It 

 decomposes into a somewhat sandy nnfertile soil mnch 

 favoured by the wild Custard Apple. Mnch of the Tundi- 

 Parasnath range is composed of it. It is also common about 

 Markacho and over most of northern Hazaribagh and into 

 Palamau. In Palamau it is found on the Kuru ^hats, in 

 the Betlah forest and numerous other places. The Koderma 

 hill is composed of gneiss, but mica schists (submetamorphic) 

 are here most abundant. Pegmatite is a handsome crystalline 

 granito with large pink masses of dull felspar and translucent 

 quartz. It is often met with (especially in Hazaribagh) and 

 occurs apparently overlying ("probably intmded into) the gneiss 

 on tho Sitagarh hill near Hazaribagh station between Banki and 

 Barwadib, at Chorparan, and in Koderma among other places. 

 Pegmatite is said to occnr in Hazaribagh in dykes in. which 

 the workable mica is found. 2 Mica is extensively mined in 

 Koderma and the vicinity. On ridges about Pachamba a 

 form of quartz schist outcrops consisting of almost pure 

 quartz with cavities lined with quartz crystals. 



The pats on the western boundary of Ranchi and in 

 Jashpur owe their flat-topped appearance to a horizontal layer 

 of trap rock : 3 there is said to be but a small depth of soil 

 on the top in which forest trees used to grow. 4 



1 A pepper-and-salt looking rock, very crystalline on fracture bnt 

 weathering black op deep grey-brown. Under the lens it appears to be 

 composed of small blackish crystals of Hornblende and white crystals of 

 quartz intimately associated. 



2 Bat the word pegmatite is uBed here in a somewhat different 

 sense as a coarse mixture of quartz, felspar and mica. It often contains 

 tourmaline, of which some fine specimens are found in the Koderma 

 mines. 



3 Vide Gazetteer. This capping rock of the pats is however elsewhere 

 referred to as laterite (Memoirs of the Geological Survey, Vol. VIII. The 

 Daltonganj Coal-field, by W. H. Hughes). Probably the two rocks axe 

 associated as is so often the case. 



< Vide p. 2. 



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