I recently found a book exclusively about the construction of the sidewheel steamer
Beaver (1835) commissioned by the Hudson's Bay Company for use in the Pacific Northwest. The book was so tedious,....boring..more like e textbook, that I put it aside before completing it...
Today I remembered I had seen
Materials Lists in the book for many ..if not every piece of wood and metal used in the construction of that boat and her (2) engines.
There it was: 
Every shaft, and dynamically "stressed" part in the engine was made of Wrought Iron. Other metal pieces..according to it's intended purpose, used Cast Iron, Brass, Bronze, Lead, etc.
I NOW have
NO Doubt that the propeller in question..and its shaft were made of wrought iron...not plain cast iron. For those of you who really want to torture yourself, below is a great article on wrought iron. Plenty of good technical stuff..
PS: I get an extra
Adult Beverage tonight before dinner, for this discovery.
NB
http://en.wikipedia.org/wiki/Wrought_iron