WOODMAN : GOLD-BEARING SLATES OF NOVA SCOTIA. 381 
places the successive layers or generations of growth can be seen 
distinctly, separated from one another by films of impurities or by 
differences in the alignment of the layers of quartz. 
In regard to the origin of the bedded veins, two views have been 
held, as noted in the historical portion of this paper. The possi¬ 
bility that all the gangue was deposited as a mechanical or chemi¬ 
cal precipitate in open water was early denied, and since 1870 has 
not been defended. Fissures which extend above and below the 
main veins, crossings from one stratum to another, and horses of 
country-rock enclosed in the quartz are irrefutable arguments 
against this view. 
There is another hypothesis, however, which it would be well to 
consider, although it has not appeared in print before. The sug¬ 
gestion has been made that the veins began as films of sedimentary 
silica, and that they have grown by secondary deposition of mate¬ 
rial which has entered in solution, in the usual manner. There 
certainly has been growth, amounting in some instances to much 
more than the original thickness of the vein, and subsequent to its 
first formation. But where are we to look for films of silica 
deposited in the sea, and where not? Is such a primary layer 
present throughout the length of a single vein? If so, especially in 
the case of the longest ones, there must have been a remarkable 
uniformity of conditions on the sea-bottom; if not, considerable 
portions were formed by ordinary methods. Moreover, where the 
growth of the veins can be studied in the field, the evidence is of 
continual accretion inward, on both sides, as in other fissure-veins, 
and not from a central primary layer outward. In addition to this, 
the field conditions do not point to a sedimentary origin of any of 
the quartz. We know that silica can be dissolved, to an appreciable 
extent, in water of ordinary temperatures; but deposition of the 
substance in continuous sheets of some size would require a previous 
•concentration of material from a larger region than it is easy to 
credit. Again, such a substance of necessity could be deposited in 
a pure state only in places where no mud and other coarser foreign 
particles were being dropped. i r et we find abrupt transitions from 
silica to slate, and from silica to coarse sand, the particles of which 
must have been deposited in water having a very appreciable 
motion. 
It seems as though no more proof than has been given by previ¬ 
ous writers is necessary to show that these are fissure-veins, and 
