from Ruge Rules
The Rule: In the not only . . . but also construction, the two items connected must be similar in kind.
Wrong: He not only painted the "Annunciation" but also [painted] the "Mona Lisa."
Right: He painted not only the "Annunciation" but also the "Mona Lisa."
Wrong: He not only played for Washington but also for Detroit and Pittsburgh.
Right: He played not only for Washington but also for Detroit and Pittsburgh.
Wrong: He not only coached soccer but also tennis.
Right: He coached not only soccer but also tennis.
Right: He taught not only physics and chemistry but also algebra and geometry.
Right: He not only taught five periods a day but also coached three sports.
(This falls under Harbrace's hugely important Chapter 26: Parallelism)