82 KANSAS CITY REVIEW OF SCIENCE. 



In opposition to the theory that lavas come from the liquid interior, is a the- 

 ory supported by many geologists who suppose that the seat of volcanoes is in the 

 deeply buried sediments. The process of metamorphism, which I have attempt- 

 ed to describe, would doubtless generate great quantities of gases. Much of the 

 salt of the sea water contained in the sediments would give up its chlorine to form 

 chlorhydric acid, which is a gas. Large portions of water would be vaporized. 

 Carbon di-oxide would also be given off from many carbonates. These gases 

 would be held by the superimposed strata until the pressure became so great that 

 they would force their way out through fissures in the rocks, forming trap dikes, 

 or through true volcanoes. It is only reasonable to conclude that in so doing 

 they would force great quantities of the liquid sediments before chem. 



There are many facts which support this theory of volcanoes. 



1. The usual escape during eruptions of carbon di-oxide, of chlorhydric and 

 sulphydric acids, all in the form of gases. 



2. The fact that the lavas of different volcanoes vary so much in composi- 

 tion ; also that the lavas from the same crater vary greatly at different eruptions. 



3. Some lavas contain hydrous compounds which, according to the theory of 

 the cooling globe, could not exist in the original molten interior. 



4. The theory demands the extensive generation of gases in sediments, while 

 they are comparatively new. As soon as the deposits were thick enough to raise 

 the isothermal horizon, action would begin. In the course of time a sort of chem- 

 ical stability would be formed, gases would cease to be evolved, and the cause of 

 eruptions would be removed. The facts correspond to this. The Appalachian 

 system, which is the oldest on the continent, has long been free from vol- 

 canoes. The much more recently formed Pacific ranges still have a few, while 

 the Oceanic Islands, around which sediments are now being formed, are the scenes 

 of frequent .eruptions. 



I am inclined to think that this last theory is the proper one to account for 

 all modern volcanoes. Its causes are surely adequate to the effect. 



Some idea of the force of gases under pressure may be formed from the nu- 

 merous examples in the Pennsylvania oil regions, where water was forced to a great 

 height by that means. It is reported that from one well the water and oil were 

 forced to a height of 180 feet. It probably reached from 125 to 150 feet. But 

 this came from a very short distance below the surface in comparison with the 

 thickness of sedmientary deposits. 



In early geologic times, when the crust of the earth was much thinner, and 

 the contraction from cooling much more rapid than now, eruptions from the in- 

 terior would be no great wonder. But at the present time the liquid mass, if ex- 

 isting at all, must be very far beneath the surface. Hopkins has calculated that 

 the minimum distance to the molten interior must be fully 800 miles. Hennessy 

 assigns 600 miles for the maximum thickness of the crust. However this may be, 

 it is very doubtful if anything from beneath the sedimentary deposits is brought 

 up by modern volcanoes. 



