Here is what I don't understand,the words in bold. It is from 'Baker's blue-jay yarn' by Mark Twain.
When his head come up again he was just pale with rage. He says, 'I've shoveled acorns enough in there to keep the family thirty years, and if I can see a sign of one of 'em I wish I may land in a museum with a belly full of sawdust in two minutes. He just had strength enough to crawl up onto the comb and lean his back agin the chimbly, and then he collected his impressions and begun to free his mind. I see in a second that what I had mistook for profanity in the mines was only just the rudiments, as you may say.
I know every word of the sentence in bold, but I think the author is saying something implicit. What I'm guessing is,the bird is swearing because of his anger and the speaker thinks that the bird's swearing is much harsher than he has ever heard among people in the mines.