Riffs - These are the kind of song where you have a cool pattern and play it over and over, leading into another riff and another, etc.
Example - "Enter Sandman" by Metallica. The opening riff is pretty famous.
Chord Progressions - This is the kind of song where you play a set of chords. You can switch to another set for the chorus or bridge, but it's strumming chords instead of a specific riff. Example - "Knockin' on Heaven's Door" by Guns n' Roses. The main part is G, D, C x2.
This "layering" method of songwriting you have seems to be riff oriented, where you play a specific pattern (riff) over a rather driving rhythm.
Personally, I prefer chord progression songwriting, because they tend to be a lot more open-ended as to improvising a solo and what you can do with the rhythm.
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster
- Aqua Teen Hunger Force, The Universal Re-Monster
