It finally hit me--the difference between city shadows--or maybe Paris city shadows--and country shadows.  

Country shadows--Edward Thomas, leafy, bobbing, irregular, trembling etc.

City shadows--all straight lines, vertical, horizontal, angled, according to the planes of buildings. No vegetation within sight. Hard-edged, precise, moving in ways that could be plotted across the surface of buildings. Sundials.

Cubistic. Obviously. If Baudelaire is the originator of the city poem--as some would have him, maybe the city poem engendered Cubism, with its overlapping plane surfaces. Just a thought. Because the weather has been nice. Good for shadows.