A bog composed primarily of sphagnum moss and decaying matter.
The term 'muskeg' is most often used for some areas in North America; similar places elsewhere in the world are often just called bogs. This 1927 newspaper article tells of two moose caught in muskeg (they were rescued).
"Much of the way, great fingers of muskeg reached through the spruce like fairways - soft, morassic, mosquito muskeg, virtually construction-proof." - John McPhee, Coming in to the Country
Etymology: 1800s, Cree: maskek, low-lying marsh.