How did Scrooge McDuck make his money?

Scrooge had worked his way up the financial ladder from humble immigrant roots. Firstly, he took up a job polishing and shining boots, and was enraged when a ditchdigger paid him with an 1875 US dime, which was useless as currency in 19th century Glasgow. However, the coin inspired him to take a position as cabin boy on a Clyde cattle ship to the United States to make his fortune at the age of 13. In 1898, after many adventures he finally ended up in Klondike. There he found a golden rock the size of a goose's egg. The next year he had made his first $1,000,000 and bought the deed for Killmule Hill from Casey Coot, the son of Clinton Coot and grandson of Cornelius Coot.

It is possible that Scottish-American industrialist Andrew Carnegie, who left his country for America at age 13 as a near-penniless immigrant teenager and eventually became the world's second-richest industrialist of his era, served as a model for Scrooge, who also immigrated at 13 according to Disney canon.