To what parts of the earth are these undulations limited?
What condition of the surface may be regarded as resulting from this cause?
What is the class of rocks most obviously referable to volcanic agency?
How do the trap rocks differ from ordinary lavas?
Why are they not vesicular?
Why more crystalline?
Why were cones never formed?
What is the proof that the granitic rocks have once been in a melted state?
Why does not the mass of melted rock below the surface retain permanently its liquid form?
Why does it, on cooling, become more crystalline than lava?