On the Geological Distribution of Gold. 37 



Superior Fluvials carrying Gold ( alluvial detritus). — After 

 the several arrangements completed during the Pleistocene 

 period, we may imagine what an immense lapse of time must 

 have been required for the reconstruction of our globe's 

 exterior, considering its condition at this time. In some 

 districts where the last or superior stratum of argillaceous 

 matter settled several hundred feet above the first layer of 

 auriferous materials, buried at the beginning of the epoch, 

 and in others, where the last mass of basalt flowed on 

 to cover and secure the treasures of Australia.* In fact, 

 at the close of the preparatory operations of denuding the 

 earth's surface, desolation prevailed, and after the levelling 

 operations had been completed, we may fairly imagine that 

 the aspect of our planet was just about the same as 

 at the beginning of the epoch we contemplate — nothing 

 but a bare naked surface, the monotony which reigned 

 being only interrupted by the sound of the gradually 

 reduced waters. We may now suppose that the meteoro- 

 logical agencies had also abated. 



But this quietude was once more to be interrupted, the 

 agency of water being again required. Immense floods 

 re-appeared with the object of forming many of the exist- 

 ing outlets for running waters, which now exhibited them- 

 selves but as small brooks passing through wide dales. 

 These operations are well illustrated in several localities 

 of Australia, not very distant from the sea-coast, where 

 the trap and basalt beds have been thus furrowed. These 

 rocks are sometimes well defined at an elevation of more 

 than 200 feet above the actual water- course, which enables 

 us to recognise the trap topping the ancient gravel-beds. 

 These gravel-beds, by the fluvial action alluded to, have been 

 changed into hillocks, called " gravel-hills," some of which 

 present very abrupt outlines, and are now covered with soil, 

 well grassed. Under these masses of fragmentary accumula- 

 tions, mostly quartz, water-worn and well-rounded, the stratum 



* The basalt and trappean rocks, covering these fluvial depositions, 

 present extensive plains, the vegetation of which is supported by the decom- 

 position of the rocks themselves. No moving waters have aided these 

 accumulations of sod, which contain silicates of alumina and iron. These 

 rocks are of a posi-Pleistocene date. In some districts good illustrations 

 of the perfect decomposition of granite exist, showing the gradual chaDge of 

 the solid rock into a plastic clay or silicate of alumina, in which the crystals 

 of quartz and mica are well defined, and this even to a depth of several feet ; 

 a scanty black sod covering the top of the decomposed granite. 



