GEOGRAPHICAL DISTRIBUTION. 43 



IV.-GEOGRAPHICAL DISTRIBUTION. 



Pegmatites are known at a very large number of places where the 

 old crystalline rocks have been exposed in India. Presumably, large 

 quantities of the same rock are also concealed by the extensive mantles 

 of younger sedimentary strata and the great sheet of Deccan Trap- 

 Nevertheless, the pegmatites are not always mica-bearing, or only 

 contain mica in small and consequently valueless crystals. In the 

 following pages only those occurrences are described which have 

 yielded mica approaching a marketable size. Some of these, indeed 

 most of them, have not been worked hitherto with profit; but it is 

 undesirable to omit them from the list, for they have of necessity been 

 exploited but superficially, and it is well to keep in mind every known 

 occurrence of possible value. 



A glance at the list of districts will show that the known occur, 

 rences of marketable mica are practically, and the paying localities 

 strictly, confined to the Peninsula. The Extra- Peninsular portions 

 of India are either covered with younger sedimentary deposits, or 

 the crystalline rocks have been so thoroughly deformed by pro- 

 found earth-movements that all large crystals of mica have been 

 too seriously mutilated to be of commercial value. It has already 

 been pointed out that our experience in India, which is capable of 

 such a simple explanation, is exactly paralleled by the distribution 

 of mica-mines in other countries : only the few areas which have 

 withstood the folding movements of the past, and which appear to be 

 specially stable portions of the crust, are being worked for this valu- 

 able mineral. The belt of crystalline rocks forming a stable Vorland 

 on the eastern flanks of the Appalachian mountain range in the United 

 States, and presenting to that mountain range a relation corresponding 

 to that existing between Peninsular India and the Himalayas, is also 

 rich in valuable mica and the most formidable competitor of India in 

 this respect. Exploration of the great stable mass of Central and 

 Eastern Africa will most probably reveal good pegmatites ; the essen- 

 tial conditions of geological stability exist there on a great crystalline 



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