356 RESUME AND THEORETICAL DISCUSSION. 
manifestations of volcanism, accompanied by ejections of lava, as, for in- 
stance, along the greater portion of the Appalachian Chain, and especially 
on its eastern border, no definite statement can be made in regard to the 
geological period of the metalliferous impregnation. It would appear, 
however, that the evidence is, on the whole, in favor of this having taken 
place at the time of, or shortly after, the upheaval of the ranges themselves. 
To prove that the rocks of such ranges as the Appalachian and Scandi- 
navian, which are surrounded by entirely unaltered Cretaceous and Tertiary 
strata, have been the scene of extensive chemical reactions during those 
later periods would be a difficult task.* Under any circumstances, there is 
no basis for Murchison’s idea that gold was — to use his own words — “ the 
last formed of the metals”; for the impregnation of the quartz veins, or rather 
its segregation, at the same time with the quartz, into veins or vein-like 
masses, was merely a collecting together of particles previously existing in 
the rock, and not by any means a new creation of them. 
On the purely chemical question, by the aid of what solvent the golden 
particles were carried into the position which they occupy, or have once 
occupied, in the veins, no light seems thus far to have been thrown by the 
investigators who, in various parts of the world, have occupied themselves 
with this problem. That the gold and the quartz were introduced into the 
vein-fissures or segregated into vein-like masses contemporaneously with each 
other, would seem, from the manner in which the two substances occur 
together, to be beyond doubt. Why they thus occur, or why this metal is 
so rarely found in any other gangue,—as, for instance, calcite, — is a question 
which cannot yet be answered. Neither has any chemist been able to advance 
the first step toward an explanation of the fact that native gold never occurs 
otherwise than as an alloy with native silver. ) 
Some other problems have engaged the attention of those who have made 
a special study of the chemistry and mineralogy of gold regions. One of 
these is the apparently commoner occurrence of nuggetsT of large size in the 
* The most extraordinary of Murchison’s theories is that held by him in regard to the relative value of 
silver and gold, which he thus sets forth in the last edition of ‘‘Siluria” (p. 475): ‘‘ Before quitting this 
theme, I would simply say, as a geologist, that Providence seems to have adjusted the relative value of these 
two precious metals for the use of man, and that their relations, having remained the same for ages, will 
long survive all theories.” One knows not which to wonder at most, the idea here expressed, or the fact 
that it is put forth as a geological statement. 
+ “Nugget” seems now to be the most generally accepted term for a ‘‘sizable” rounded piece of native gold. 
It appears to be a word of Australian origin, and is the equivalent of the Spanish ‘‘ pepita” (seed, pip ; pépite 
in French) or ‘‘chispa”’ (a spark or brilliant). ‘*Scad” is the American for nugget, but, so far as the writer 
knows, of recent origin, and not in general use, even among the miners. 
