This is a witty and fond recollection of a bubble. Twain and a friend were millionaires -- for ten days. Chastened, Twain got a real job and invested prudently and was about to sell out for about $100K in Civil War dollars -- not a fortune, to be sure, but enough to retire on if he chose. Then the silver mine stocks all crashed, and his stock was the same fairy-gold wallpaper that so many internet veterans own.
It's nicely observed. When Twain recalls the stagecoach and the pony express, he's writing about technologies that shaped the world but that lasted only eight or ten years before they were replaced by faster technologies with better throughput. The internet generation didn't invent internet time, it simply made it faster.
But George's [revolver] was a reliable weapon, nevertheless, because, as one of the stage drivers afterwards said, 'If she didn't get what she went after, she would fetch something else.' And so she did. She went after a deuce of spades nailed against a tree, once, and fetched a mule standing about thirty yards to the left of it. Bemis did not want the mule; but the owner came out with a double-barreled shotgun and persuaded him to buy it anyhow. It was a cheerful weapon.