The Collaborative International Dictionary of English v.0.48:

Subsultory \Sub*sul"to*ry\, a. [L. subsilire, subsultum, to
   spring up; sub under + salire to leap.]
   Bounding; leaping; moving by sudden leaps or starts. [R.] --
   Sub*sul"to*ri*ly, adv. [R.]
   [1913 Webster]

         Flippancy opposed to solemnity, the subsultory to the
         continuous, -- these are the two frequent extremities
         to which the French manner betrays men.  --De Quincey.
   [1913 Webster]