What is the general law of increment of temperature?
At what depth would most mineral substances be melted?
How is this conclusion confirmed?
What was probably the original state of the mass of the earth?
What other explanation may be given of this interior heat?
What is the elastic force upon which volcanic phenomena depend?
Upon what does the fluidity of lava depend?
Upon what does its porous structure, when cooled, depend?
Why are volcanoes situated near the sea?