Since the pebbles embedded in the real adobe bricks referenced in this painting were small and didn't seem to call for quilting, I thought the slightly larger pebble/stones placed between a few layers of bricks, might look fine 'unquilted' too. So the pic above is where we start from. The small stones nearer the top of the picture would at minimum require an outline stitch as would be often be done around an appliqued piece to make it 'stand up and stand out!
I think I will take it one step further really knocking down the dark area around stones and in dark shadow. This seems to produce a rather refined finish. I used a pewter colored thread as opposed to black as it seemed easier on the eye than a high contrast black would have created. After all, my goal is to keep the eye on the main subject ( 2 little girls on a stoop) rather than drawn to quilted bricks in the outer edges of the quilt. Soooo much to think about. ;-)