104 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
It is not unlikely that the formation of the columnar channels of 
gas escape accounts for the existence of certain peculiar features 
which may he noted in many mineral veins. In these veins we 
commonly find the ore-bearing materials are arranged in chutes or 
chimneys which extend in a generally vertical direction, these por- 
tions of the fissures in these chimneys being often rich in peculiar 
minerals while the parts of it on either side are barren or contain 
much less of the substance. In such cases it seems probable that 
the fissure was filled with water up which the gas impelled a por¬ 
tion of the fluid that-was rich in the mineral material, the principle 
of the upgoing being the same that we have noted in other instances 
of gas ascent. 
In the necessarily brief discussion of the movements of gases 
through the crust of the earth many facts bearing on the problem 
have been left without consideration. Enough has, however, been 
set forth to make it probable that the principle or as some would 
term it the law of these ascending movements is that which is 
shown in the ascent of columns of bubbles in gas — charged water. 
The likeness in the general features of these groups of actions, 
the shock fountains, the ordinary springs, and the volcanic pipes, 
makes it seem most likely that they are all manifestations of the 
same principle, however much the magnitude of the work may 
differ. 
Before closing this paper it will be well to give some considera¬ 
tion to the conditions which determine the horizontal movements of 
gases on their way towards the paths of escape which the vertical 
shafts provide for them. One of these is indicated in the account 
of the shock fountains which were observed in the field affected by 
the Charleston earthquake, where, as has been noted, the thicker the 
section above the line of gas generation the more widely separated 
were the vents. It is evident that the deeper the impeding cover¬ 
ing the further the gases would be driven to move in a generally 
horizontal direction in order to enter the vertical channels of escape, 
for the reason that a less energetic thrust might in that way prove 
effective than would be competent to overcome the resistance of the 
superincumbent strata. That the vapors discharged from the 
volcanoes are derived from a considerable distance, that these 
vapors make their way horizontally, driving the molten rock before 
them for distances of scores if not hundreds of miles, is shown by 
the large amount of the discharge both of vapors and solids which 
