How is coal shown to be of vegetable origin?
Why will the drift wood of the sea accumulate in particular localities, and why will it sink?
Why will it become buried beneath earthy matter?
How is it known that wood thus buried will, at length, become lignite?
How is lignite converted into mineral coal?
What is the proof of it?
Have beds of coal been formed at other periods, besides the carboniferous?
Is it probable that coal-beds are now forming?
How did the flora of the carboniferous period differ from the existing flora?