360 RESUME AND THEORETICAL DISCUSSION. 
With regard to the manner in which the gold in the quartz loses its char- 
acteristic forms, so as to become transformed into the smooth rounded masses 
occasionally found in the placer mines, there seems to be no theoretical 
difficulty. In the first place, however, it may be stated that by no means 
all the nuggets have this character. Many of them exhibit more of their 
original character than would be expected to be found remaining after ages 
of pounding between the boulders of the gravel. This is particularly true of 
specimens collected by Professor Pettee from the hydraulic mines during his 
last year’s investigations, and which have been been carefully examined 
by Mr. Wadsworth and the present writer. The same fact has also been 
stated by Mr. Ulrich — who appears to be a close observer —in regard to 
the Australian nuggets.** There seems to be no doubt that a scraggy — 
to use a common miner’s term— piece of gold can be transformed into a 
rounded smooth nugget by a sufficient amount of the right kind of rubbing 
and hammering, which must have taken place as these great piles of detritus 
were being shifted from place to place by currents of water. -Some of the 
specimens collected exhibit in the most interesting and convincing manner 
the transitional form between the rough crystalline form and the smooth 
rounded one. One in particular, from an unknown locality, purchased 
by the writer in a shop at San Francisco, has one side almost perfectly 
smooth, and rounded edges turned over upon the back, which itself is 
covered with crystalline branchings, still retaining a large part of their 
original delicacy. It is evident, in this case, that the specimen has been 
protected on one side, while the other has been subjected to abrasion and 
pounding, the result being a nugget, presenting at the same time and in 
most remarkable perfection, the characteristic forms of quartz gold and 
placer gold. 
That the masses of gold, when they have been released from the quartz 
veins and have begun to be rolled about in the gravel, could by any possi- 
bility be so situated as to become subjected to any chemical influences by 
which their mass could be enlarged, seems — to the writer, at least — highly 
improbable. That occasionally pieces of the metal may be united by pres- 
sure or by hammering between the gravel boulders, and that thus a larger 
mass may be formed by the union of two or more smaller ones, through 
purely mechanical agencies, seems not impossible; and some observations 
of Mr. Wadsworth appear to corroborate this view. 
* See R. Brough Smyth’s ‘‘Gold Fields and Mineral Districts of Victoria” (1869), p. 360. 
