1856.] Economic Geology of Assam. 341 



poora, boulders of this description are found, but thej have been 

 deposited there ages ago, probably from the vicinity of the limestone 

 strata holding the decomposing property. 



27. Similar to proceeding (unbroken). — Ditto ditto. Ditto ditto. 



28. Deposit from Brahmaputra after heavy rain. — Found princi- 

 pally in the inland offshoots and churs of the Brahmaputra. It is 

 of the nature of rotten stone. This is found sometimes in large 

 quantities and requires to be scraped off as the river falls, and is 

 evidently washed down from the decomposing rock associated with 

 the limestone. 



29. Washed from calcined lignites, also of the nature of rotten 

 stone or crocus martis. — Large masses of true lignite are imbedded 

 in the soft sandstones of the Booree Dehing, and large quantities 

 of the same kind but less compact are to be procured in the bed of 

 the Dhunseree. — From the true lignites of the Booree Dehing a sub- 

 stance suitable for pigments, as also for polishing metals, is procur- 

 able. The decayed fossil wood of the same localities (from a state 

 of chert or flint) also supplies excellent rotten stone capable of 

 giving the highest polish to precious stones. The Burmese lapi- 

 daries invariably use this substance in their lapidary work. 



30. Compact rock, supposed dolomite or magnesian limestone. — This 

 limestone is found both in the Brahmaputra and Dora Panee, but 

 principally in the latter stream, and seems to be associated in situ 

 with the accompanying granite and felspar rocks, forming the Kaolin 

 clay, and in this case is a valuable addition to these as containing 

 magnesia. This is procurable along with the Eooknunsee Peeta 

 and decomposing granite and felspar rocks of the lower ranges, 

 Upper Brahmaputra, and probably thus associated causes the decom- 

 position of these rocks ; some of the varieties of this marble, are 

 yellow, streaked with dark colored delineations. All the rocks of 

 this locality contain a quantity of very bright colored whitish 

 pyrites, or sulphate of iron — the primitive lime marble in particular 

 containing large quantities of bronze coloured and white pyrites of 

 all the varieties of this mineral. 



31. A variety of No. 30.— Ditto ditto. Ditto ditto. 



32. A variety of JVos. 30 and 32. — This is also found in the Upper 

 Brahmaputra of a purer white than the rocks of the same kind in 



