96 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the gases which they contain. Bored wells and also often mine 
shafts show us that the greater part of the rocks which have not 
advanced in their metamorphism to the crystalline state are to a con¬ 
siderable extent charged with gases under high tension which seek 
to avail themselves of an opportunity to pass upward. It is only 
where the metamorphic processes have gone very far that the rocks 
cease to yield gas; it would indeed be from this point of view a rea¬ 
sonable arrangement to divide strata into those which have and 
those which have not parted with the gases which are necessarily 
formed in them after their deposition. 
I have already incidentally alluded to the point that many if not 
the most of these discharges of waters through bored wells which are 
commonly termed artesian are most reasonably accounted for on the 
supposition that the ascensional force is due to the expulsive energy 
of the gases they contain. There are undoubtedly instances in which 
the flow is due to the true “ head ” of water, in other words, the 
action is that of gravitation, but in other cases, as, for instance, in the 
wells of the southern plain land and the most of those in the Missis¬ 
sippi Valley, the supposition of a sufficient gravitative impulse to 
account for the ascent of the water above the level of the ground 
appears to be inadmissible, while the gaseous contents clearly show that 
the cause may be found in their presence. This difficulty, which, though 
not formally stated, has led geologists to suppose that ascensional 
energy was due to the artesian principle, lies in the fact that the 
water discharged from the wells, though it may come from beds which 
were made beneath the sea, is not in most instances sea water, but is 
rain water which has been more or less intermingled with materials 
which have been contributed to it during its sojourn in the rocks. 
For a long time I saw no way out of this difficulty, but recently a 
hypothesis as yet unverified has suggested itself as a means of explain¬ 
ing the point. This I will now briefly present. 
When a section of strata laid down beneath the sea becomes elevated 
above the ocean level, the interstices of the rock retain for a greater 
or less time the water which was stored in the crevices between the 
grains of sand or mud. In some cases where before it was uplifted 
the bed had been covered by very dense impervious deposits, this 
water of the ocean may be indefinitely retained, as in the case of some 
of our Silurian rocks which discharge through borings which are made 
into them the ancient brines in which they were formed. Generally, 
however, the rock is sufficiently pervious to permit the rain water to 
