Context:  Twain is recalling a meeting of the Monday Evening Club hosted by Rev. Frank Goodwin in Hartford – circa 1877 when Jacob would have been about age 40.  At these meetings, each member in turn made a short presentation.  On this occasion, the subject was Dreams.  Here’s what he says about Jacob:

Then came the late Colonel Greene, who had been a distinguished soldier in the Civil War and who at the time that I speak of was high up in the Connecticut Mutual and on his way to becoming its president presently, and in time to die in that harness and to leave behind him a blemishless reputation, at a time when the chiefs of the New York insurance companies were approaching the eternal doom of their reputations.  Colonel Greene discussed the dream question in his usual way—that is to say, he began a sentence and went on and on, dropping a comma in here and there at intervals of eighteen inches, never hesitating for a word, drifting straight along like a river at half bank with no reefs in it; the surface of his talk as smooth as a mirror; his construction perfect and fit for print without correction, as he went along.  And when the hammer fell, at the end of his ten minutes, he dumped in a period right where he was and stopped—and it was just as good there as it would have been anywhere else in that ten minutes’ sentence.  You could look back over that speech and you’d find it dimly milestoned along with those commas which he had put in and which could have been left out just as well, because they merely staked out the march, and nothing more.  They could not call attention to the scenery, because there wasn’t any.  His speech was always like that—perfectly smooth, perfectly constructed; and when he had finished, no listener could go into court and tell what it was that he had said.  It was a curious style.  It was impressive—you always thought, from one comma to another, that he was going to strike something presently, but he never did.  But this time that I speak of, the burly and magnificent Reverend Doctor Burton sat with his eyes fixed on Greene from the beginning of the sentence to the end of it.  He looked as the lookout on a whaleship might look who was watching where a whale had gone down and was waiting and watching for it to reappear; and no doubt that was the figure that was in Burton’s mind, because, when Greene finally finished, Burton threw up his hands and shouted, “There she blows!”