48 PRKSIJIEXTIAL ADJJRESS SECTION B. 



solution of tlie problem, since there is a single intrusion, 

 entirely similar in every way to tlie otliers, wliicli cuts 

 throug-li the reefs near the seventeenth level, thus assig-ning 

 their formation to the period during which the dykes were 

 being- intruded. 



What is really of most value in discussing ore deposits 

 is unquestionably detailed field work, influenced as little a.^ 

 Ijossible by theoretical considerations. As an example may 

 be cited the close examination of the AVitwatersrand goldfield 

 carried out by Dr. Mellor. It is true that Dr. Mellor has 

 made certain theoretical deductions from his observations 

 which I have publicly dissented from. It is for this very 

 reason, and also on account of the attacks recently made 

 upon the official interpretation of the Rand's g-eological 

 structure, that I specially desire to emphasise the importance 

 of such a detailed scrutiny of these great gold deposits. We 

 may not be at all inclined to agree with the conception of 

 the Rand gold as being of alluvial origin, but there can be 

 no two opinions on the part of any unbiased observer 

 regarding the value of the held work itself. It may not be 

 out of place to add that people would do well to think twice 

 before accepting the ideas of a school who do not object to 

 be described as " unorthodox geologists." In particular, 

 attention may be drawn to tlie absolutely unequivocal declara- 

 tion recently made by Dr. Rogers that the reefs of the East 

 Rand can be followed without any break right through the 

 point where a fault is postulated by the unorthodox, which 

 is absolutely necessary to substantiate certain of the 

 hypotheses which they have advanced. 



I do not at all suggest that it is desirable to fetter the 

 mining geologist in any way. By all means let him theorise. 

 jSTevertheless, it cannot be gainsaid that his theories are worse 

 than useless if they cause him to overlook any important fact. 

 To be perfectly frank, I am strongly of ojiinion that the chief 

 function of the mining geologist lies in the correct inter- 

 l)retation of structural features. Thus, in the study of ore 

 deposition, the nature of the fractures that have determined 

 the position of the ore-body is of the first importance, if it is 

 related to fracturing, or, on the other hand, the fact that a' 

 particular occurrence has not been so determined is equally 

 important. Another problem which it is necessary to solve 

 is the relation, if any, which exists between the ore-body, 

 or the richer portions thereof, to adjacent roeks or rock 

 structures. This may involve a nice discrimination between 

 the essential and the accidental features in the associations 

 of the deposit, and although such associations have been 

 correctly diagnosed in certain cases — for instance, that of the 

 well-known " indicators " of the Ballarat goldfield in 

 Australia — without geological assistance, it is probable that 

 close study by trained observers would lead to the recognition 

 of many similar but less obvious examples elsewhere. Even 

 more important may be what is perhaps to be regarded as 

 applied mineralogy, namely, the investigation of the extent 

 to wliicli secondary processes have influenced values in the 



