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other formations. For instance, most of the hot springs of 
the Pyrenees exist in districts where the granite comes in 
contact with the cretaceous formation ; those, too, of Marien- 
bad rise at the point of junction between the granite and 
transition strata. It is easy to understand that the point of 
junction between primary and sedimentary strata should be 
favourable to the emission of springs, from the fissures which 
are likely to exist there, in consequence either of the decom- 
posing influence of the eruptive on the sedimentary rock, or 
from the contraction produced by the cooling of the former. 
It has been suggested that the origin of metallic veins, 
which generally occur in the same situation, may have 
been due in past ages to hot springs charged with the con- 
stituents of these veins, which have gradually deposited them 
in the fissures through which they were emitted. Before 
leaving the subject of the temperature of springs, it should be 
mentioned that some authorities, and amongst them more 
particularly Dr. Yolger,* maintain strongly that all the phe- 
nomena of thermal springs are explicable without any 
necessity of invoking the hypothesis of a central heat, re- 
ferring them to the combined effects of chemical decomposition, 
pressure, and motion. 
There is one feature of many springs which deserves a 
passing notice, and that is, the phenomenon of intermission. 
The intermission may be either partial or complete. In the 
former case the spring only diminishes in activity at certain 
periods ; in the latter, it ceases altogether at times. The 
period of intermission varies greatly in different springs. 
That of Poterbrunnen, at Paderborn, in Westphalia, ceases 
for 6 hours, and then flows again for 6 hours more with such 
energy as to turn three mills. Another spring at Pontarlier, in 
the Jura, intermits every 6 minutes. Another at Fontestan, 
near Mirepoix, flows for 36 J minutes, and then ceases for 
334 minutes. Another at Colmar, in Prussia, flows twice in 
the 24 hours, for 7 hours each time, and ceases twice for 5 
hours. We have two intermittent springs in England, — that 
at Giggleswick, nea-r Settle, in Yorkshire, and Tideswell, in 
Derbyshire. Both of them flow for a few minutes only, and 
both rise in the mountain limestone. But the most interesting 
case of intermission is that of the well-known springs of the 
Geysers, in Iceland, before alluded to, the smallest of which 
flows for 15 to 20 minutes every 2 hours, and the largest only 
once in 24 to 30 hours. These intermittent ejections are probably 
caused by the irregular ebullition of the water in the pipe 
of the Geysers, giving off masses of vapour at intervals, which 
carry water up with them into the air, just as in the case of 
* “ Erde und Ewigkeit.” Frankfurt a. M. 1857. 
