12 ECONOMIC GEOLOGY. 
type has been described in Volume II as the Cambrian clay slate. 
There is little mention made of the veins, save in the catalogue of 
the specimens obtained from the Ammonoosuc district, and their delin- 
eation upon the map on page 296. The quartz is somewhat glassy, 
whitish, except where it has been stained by the decomposition of pyr- 
ites, and nearly pure. Masses of slate, crystals of pyrites, ankerite, and 
galena are scattered through it. It is common to find spangles of free 
gold in the quartz, most conspicuously at the boundary between the 
quartz and fragments of slate in it. The ankerite is a characteristic 
mineral of all the auriferous veins of the Connecticut valley clay slates. 
The question arose early as to the proper source of the gold. All that 
can be seen macroscopically is in the clear quartz. In 1869, I had the 
general average of the vein assayed, and also each constituent by itself, 
except the galena, which was of rare occurrence. The average was 
taken twice;—first, a picked sample from the vein; second, a portion of 
several hundred pounds’ weight that had been pulverized in the mill for 
practical extraction. According to Prof. C. A. Seely, the amount of gold 
in both the averaged samples was essentially the same, or $18.90 to the 
ton. Of the constituents examined separately, taken from the same 
pile, the clear quartz yielded $18.11 of gold to the ton. The pyrites 
occurring in the quartz and in the slate both yielded traces of gold, but 
not enough to be measured, the latter affording the greatest amount. 
Neither the slate nor the ankerite afforded any trace of gold. If it were 
allowable to generalize from these single determinations, it were easy to 
say that 95 hundredths of the gold comes from the clear quartz, and the 
balance from the pyrites in the vein. There is not very much of this 
mineral present, but sufficient to attract attention, and to be saved by 
some of the manipulators. Seeing a pile of this pyritiferous residue in 
the rooms of the Electro-Gold company’s mill, I begged samples for 
assay. Prof. Blanpied found no gold in it. The species seems to be the 
common bisulphuret,—not the magnetic variety, nor mispickel, which is 
auriferous in this neighborhood. 
The gold, as obtained from this vein, is very pure. I examined twenty- 
four of the returns from the mint, and found the average of them to be 
916.8 parts of gold to 83.2 of silver. This is purer than the average of 
this metal in auriferous countries; that of California is 880 in 1000; 
