THE PERSISTENCE OF WOLFRAM IN DEPTH. 245 



capping* of schists and phyllites over the Malayan granites, even if 

 they are less in number and not so extensive as those in Tavoy, 

 is insufficient ground on which to base so far-reaching a theory. 

 In view of the local differences of composition in mixed concen- 

 trates from closely related geological horizons in Burma itself, 

 we prefer to regard the cause as one connected with inherent varia- 

 tions of composition in the original magma. 



THE PERSISTENCE OF WOLFRAM IN DEPTH. 



There is little field evidence in Tavoy to furnish data regarding 

 the persistence of wolfram in depth. All that can be said is that 

 the deepest exploratory workings in granite have proved both the 

 veins and the two minerals wolfram and cassiterite which they 

 were commenced to find, but they do not go more than 400 feet below 

 the horizon of the granite contact. Veins worked for a few fathoms 

 in the soft rocks below the level of their outcrops, and detrital 

 deposits, have furnished by far the greater part of the concentrates 

 which the district has produced up to the present, and deep level 

 mining has hardly commenced. But as Dr. W. R. Jones has pointed 

 out, " it does not require artificial crosscuts to establish (the presence 

 of wolfram), for Nature has provided us, on some mines, 

 with many in the form of deep valleys, and has definitely proved. 

 in the exposed lodes, that wolfram does occur in workable amounts, 

 at depths of several hundreds of feet below the great majority of 

 the present workings.'" 1 Dr. Morrow Campbell, on the other hand. 

 does not believe that because the outcrop of a vein is seen to be 

 continuous from the summit to the base of a granite hill several 

 hundred feet high, it persists for an equal vertical depth, for the 

 slope of the hillside is usually practically parallel to and not far below 

 the original granite periphery, the overlying sediments and only a 

 very little granite having been removed by denudation. This is 

 doubtless true in some cases. In others it is not, and if there is 

 anything in the old miners' rule regarding the relationship between 

 the strike extension and the depth to which a vein extends, some 

 of the wider and well-defined veins, say in regions like Paungdaw, 

 ought to persist to very considerable depths. Dr. Campbell is 



i\V. R. Jones (15), p. 43. 



