Read it through once

On the rocks above the present city of Alton they found some rude and fantastic Indian paintings, which they describe. A short distance below 'a torrent of yellow mud rushed furiously athwart the calm blue current of the Mississippi, boiling and surging and sweeping in its course logs, branches, and uprooted trees.' This was the mouth of the Missouri, 'that savage river,' which 'descending from its mad career through a vast unknown of barbarism, poured its turbid floods into the bosom of its gentle sister.'