We attended Mountain Craft Days at the Somerset PA historical center today. One of their displays is a reproduction of a 1770's frontier homestead. Notice the construction of the fireplace and the external chimney. It's log and clay/mud. The individual explaining the construction said the chimney was deliberately built separate from the log cabin so that if there was a chimney fire it could be pulled down off the building to save the rest of the building. The fireplace is so big that he said the logs in the fireplace and chimney don't really get hot in their reproduction homestead but accidental fires were not uncommon in these homesteads.