Where can you find symbols (like these) that aren't on the legend? I see a lot of these fan like symbols: 

  

...on the Nav Canada Alaska Highway - Fort Nelson to Northway, 1:500,000 VFR Navigation Chart, but they're not anywhere on the map legend.

I presume they're marshland as they look a little similar to symbols I've seen on hiking maps, but I don't like assuming when making flight plans!..

Is there some universal reference somewhere that I don't know about? Are they indicating marshland, or are they something else entirely?
You can find this symbol in the  "FAA Aeronautical Chart User Guide"

on page 30.  

It shows as "Swamps, Marshes, Bogs"