What is the difference between magic resistance and the elemental resistances?

There are several kinds of resistances in Skyrim: magic resistance, flame resistance, frost resistance and shock resistance.

Is the magic resistance essentially just resistance to all three elements, or are there magic damage types besides those three? And are all sources of flame, frost and shock magic damage, or are there non-magical sources of elemental damage?

Magic resistance works against Fire, Shock, and Frost Damage, but it also reduces the effect of Absorb Health/Stamina/Magicka effects, magical "vulnerable to x" effects, etc.

You'll notice that you get much lower magnitudes of resist magic than you can get of resist elemental attributes for the same price. Resist Magic is the preferable choice, but you sacrifice magnitude for broad-spectrum defensive coverage.

I'm not sure if damage from standing in Oil Fires (the only non-magic source of elemental damage that comes to mind) is reduced by Resist Magic.