In reply to Kathleen Mitchell who inquired about this passage --
it is most likely the passage from Twain's autobiography relating
to the death of his daughter Susy which begins "It is one of the
mysteries of our nature that a man, all unprepared, can receive a
thunder-stroke like that and live."  See chapter 66 of _The
Autobiography of Mark Twain_ edited by Charles Neider.

Barb