The third method of gemming in river beds is less common and calls for more arduous and prolonged operations. A low, temporary, brush-wood dam is built across a stream to increase the flow of water at a selected spot. Long-handled shovels up to twelve meters or more in length with mammoty heads at the ends are employed by six to eight men to drag the river bed at a point upstream of the temporary dam. The men standing in a row across the stream scoop out a hollow by removing the sand and exposing the illam layer in the river bed. The overburden of sand and silt is carried away by the agitated water and the coarse material and the gravel comprising the illam is raked up and collected in a low ridge. This partly sorted illam is next removed in baskets to the bank of the stream and the gravel washed in the usual way. This method of gemming can only be employed when the gravel occurs at shallow depths.
The methods of mining employed are simple, almost primitive, using only manual labour and with the exception of pumps no mechanical means are used. They involve little capital outlay and are time honored methods which are quick and reasonably efficient and particularly suited to the nature and mode of occurrence of the gemstone bearing gravels. Besides, mining is seasonal and normally extends from December to May as most of the gemstone bearing lands are flooded or partly sub merged during the wet season. With sporadically distributed gravels, the use of mechanical means of excavation or dredging is not feasible. Some degree of mechanization has been introduced in recent years for the washing of the gravels.