'Scotch' is just a generic name for a certain kind of snuff, the US ones are generally of the scotch type - fine, dry and penetrating, but not to be confused with snuff that has a whisky flavouring. The name goes a long way back into snuff history, when the scots were famous for taking their dry snuff from 'snuff mulls' which are snuff boxes made from the tip of a ram's horn. There was also Welsh snuff and of course we still have the Irish variety - all of them light and finely milled.
Or
There is an old explanation given by Levi Garrett that is being lost to history as to where the term "Scotch Snuff" was made. It goes as follows. The Scotchare sometimes referred to as penny pinchers. And of course you can imagine one dressed in plaid as squeezing a coin between his fingers
to get the last value from it. This was to explain how this
tobacco
was to be used, a pinch between fingers. Now Scotch Snuff was made in
a certain way. It is made with the darker leaves and stems which are
deeper in flavor. They cure this tobacco with fire and is called "dark
fire cured". This gives the tobacco its smokey flavor.
And then my favorite:
As I remember the first scotch snuff was produced in south England, so it's kind of strange for me that now only American are making it.
The legend says that the English didn't like what they made and cast it into the waters of the Atlantic Ocean. But the snuff fought for it life with passion, defeated a lot of spooky monsters and pirates..a short brake on the Bahamas...to finally be welcomed by the Americans. The end.
Some of the terms related to snuff are ambiguous at best. Suffice to say that the American Scotch as the term is used today is a fine grind, dry, high nic content that will last forever if kept dry and blow the back of your head off if not used with care!