82 lh> American Geologist. Feb. 1891 
few small, irregular fissures, near the shrunken and compacted 
materials extending from the focus or near it. up to the bottom of 
lake Nicaragua, through which water circulated. These waters 
found access to a temperature of about 400 Fah., and generated 
aqueous vapors until their elastic force was sufficient, assisted 
most probably by other gases of greater elasticity, to cause the 
earthquakes and the sounds associated with them, from the 0th to 
the 22d instant. There were no indications observed of vortical 
motions, nor of that class of earthquakes. Neither was there any 
of the bounding or tossing up movement, nor deafening sounds of 
the explosive type of earthquakes. If the water from lake Nicar 
agua found access to the geothermal plane where the focus of the 
first earthquake was found to be. it is reasonable to conclude that 
this is the process by which are formed caverns containing liquid 
rock materials and elastic gases and aqueous vapors ; and that 
these will increase in size, quantity and elastic force, until 
sufficient force has accumulated to upheave and eject the super- 
imposed masses, in other words, commence volcanic activity, like 
volcano Tarawara in New Zealand: this activity once originated 
will continue so long as lake Nicaragua, like the lake once exist- 
ing near volcano Tarawara. previous to the eruption of that 
volcano, supplies the water necessary for its promotion. Strong 
alkaline waters at 400° Fah., in long contact under a pressure <>l 
3 or 4 miles of superimposed material will, no doubt, dissolve all 
kinds of rocks, and the dissolved material will occupy much les> 
space than when in a loosely compacted condition. Consequently 
the caverns that are formed are constantly increasing in size, 
allowing for a constant increase of the materials that promote vol 
canic energy. But earthquakes appear to have ceased in thai 
locality, perhaps because the fissures have been closed by shrink- 
age or filled with pozzuolano or other hydraulic cement. 
The facts observed during the recent earthquakes assist in 
establishing the following in reference to this class of physical 
phenomena 
1st. They frequently are the result of sudden shrinkage from 
greater contraction in the interior along certain radii than at the 
surface — Mechanical energy. 
.'ml. They mav and often do originate locally a few miles only 
