652 REPORT— 1901. 



direction, rudely disposing the comminuted auriferous quartz in ' leads ' in tlie 

 Drift. The present streams, cutting across the Drift, have more or less concen- 

 trated the gold. Profitable working of the deposit is precluded hy the ' hurden ' 

 o( large stones, by the importance of the vested interests concerned, and hy the 

 inclemency of the winter season. 



7. Field Azotes on the Influence of Organic Matter on the Deposition of 

 Gold in Veins. By J. Malcol3i Maclaren, B.Sc. 



The reducing action of organic matter on the soluble salts of gold was fairly 

 established by the researches of Henry, Percy, Daintree, Sterry Hunt, and New- 

 bery, and organic matter was considered for many years to be responsible for the 

 great majority of the auriferous vein deposits of the world. With tbe publication 

 of Skey's researches, and his demonstration of the fact that sulphides alone are 

 competent to produce complete precipitation of gold from solution, the former 

 theory was almost completely abandoned. The following cases, however, which 

 have come under the writer's personal observation, admit at least of the possibility 

 of precipitation by carbonaceous matter. 



The reefs of the Gympie Goldfield, Queensland, underlie almost at right angles 

 across the dip of the bedded greywackes, shales, sandstones, and limestones in 

 which they are situated ; but it is only where highly carbonaceous shales (the 

 ' First,' ' Second,' ' Third,' and ' Phoenix' 'slates' of the miner) are intersected by 

 quartz reefs that the latter are auriferous. The carbonaceous shales are certainly 

 pyritous ; but so also are the overlying and underlying beds in which the veins 

 are barren. 



The Croydon Goldfield, Korth Queensland, is in an area of metamorphic 

 granite, containing much graphite. The reefs are more or less enclosed within 

 walls of kaolinic matter highly charged with graphite. Where graphite is most 

 abundant have been the richest auriferous deposits. On the other hand, broadly 

 speaking, the presence of pyrites in a Croydon reef indicates poverty of content, 

 and is considered as an unfavourable indication bv miners. 



The ' indicators ' of the Ballarat Goldfield, Victoria, are thin beds of dark- 

 coloured shales and slates, formed of a carbonaceous mud and containing a con- 

 siderable percentage of iron pyrites. The main ' indicator ' has been followed with 

 few breaks for a distance of eight miles. The most profitable quartz reefs cross 

 the ' indicators ' almost at right angles, and the great bullc of the gold is found 

 where the quartz reef has crossed and slightly faulted tlie ' indicator,' little gold 

 being found at a greater distance than a yard from the intersection. 



8. The Source of Warp in the Ilumher. 

 By W. H. Wheeler, M.Inst.C.E. 



It has frequently been stated that the mud or warp in suspension in the 

 Humber is derived from the erosion of the cliffs on the Yorkshire coast, and the 

 object of the paper is to show that it is physically impossible for the detritus 

 eroded from those clifis to be carried into the Humber, and that the material in 

 suspension in the water is derived from detritus washed off" the land drained by 

 the Humber and its tributaries or eroded from their banks. 



The drainage basin of the Humber covers 10,.500 square miles, and embraces 

 Btrata of various kinds of rocks, including estuarine deposits, glacial drifts, chalk, 

 sandstone, and oolites. 



The water in the zone extending around the junction of the Trent and the 

 Ouse with the Humber, extending over a length of thirty-five miles, is very 

 highly charged with solid matter in suspension, the maximum quantity being 

 attained in the summer, when the downward flow of the fresh water 'is at a 

 minimum, the quantity then in suspension amounting to as much as 2,240 grains, 

 or nearly the third in a cubic foot of water. Above and below this zone the 



