192 Scientific Intelligence . — Geology. 
the pit, and gradually sinking the head, they experienced the 
same sensation as when held over a vat in a state of fermenta- 
tion. The quantity of evolved gas varies at different times. 
This evolution of carbonic acid gas is more striking in the vol- 
canic Eifel. On the right bank of the river Kyll, nearly oppo- 
site to Birresborn, there is a, spring named Brudelreis, a pro- 
vincial name for a boiling spring, and applied to this, because 
its surface is perpetually agitated by large air-bubbles. The 
agitation occasioned by the evolution of the gas is so great, 
that the noise is heard at the distance of 400 yards. In the 
vicinity of the basin of the spring, numerous dead birds are 
found, evidently killed by the carbonic acid which rises from 
the surface of the water. Persons who kneel down to drink out 
of the spring, are driven back by the mephitic exhalation from 
the water. Five hours from Triers, in the neighbourhood of 
Hetzerath, there is another spring, which resembles that just 
mentioned, in forming a basin, giving out much carbonic acid, 
and emitting a loud noise. Bishof and Nogerrath visited the 
Brudelreis : they heard the noise, occasioned by the evolution of 
the gas, at a considerable distance ; and found, on approaching 
their faces to the surface of the turf, in the vicinity of the springs, 
that it was covered with a layer of carbonic acid. They did not 
observe that the carbonic acid produced any deleterious effects on 
the surrounding trees or grass, although it is known that the 
moffettes of Vesuvius exert a destroying effect on the roots of the 
plants of that district. On emptying the basin, no more water 
was collected, shewing that it was rain not spring water ; but 
the carbonic acid continued to rise through the fissures of the 
rocks, and through some, with so much power, as to feel to the 
hand like the wind from the nosle of a bellows. On pouring 
a glass of lime-water into one of the fissures, it became turbid, 
and the phenomenon of ebullition, although on a small scale, was 
thereby exhibited ; but they did not ascertain if the gas was 
perfectly pu^e carbonic acid. Carbonic acid is evolved in con- 
siderable abundance, as well from volcanoes in a state of activity 
as from those which are extinct. These exhalations may be di- 
vided into transitory and permanent. The first are the most 
common meoffettes, such as those evolved from Vesuvius, and its 
vicinity, after every eruption. They appear frequently a month 
