Just for fun, Rook, could you post a few pics of your jacket? Give me a few close-ups of the jacket outside, and I may can give you an idea. Of course, there are a few general properties of leather that set apart one skin from another. G&B's website does a good job in explaining these differences:
http://www.gibson-barnes.com/Types+of+Leather/id/47/
http://www.gibson-barnes.com/Learn+About+Leather/id/43/
Generally, thin, soft, shiny, pliable leather with a small grain is lamb. Thicker leather with larger grain is cow. Stiff leather with larger grain (similiar to cow) is often goat. The smell is distinctive. These are of course, generalizations.
Today, the most common leather material used in jackets are either lamb and cow. In the early 20th century, it was goat or horse.
Disclaimer: When the top grain of leather is removed, all bets are off unless you can feel and smell it.
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