A few years ago I bought a bunch of hooks at one of Donnelly auctions from one of the largest logging tool collections in the US. Those type are generally called swamp hooks. I have been told that they were used to put under a log to give you something to pull against, but they may have had another use. There were a lot of those in the collection.
There is a similar one called a J hook that had a ring and hook on it. I cannot remember the exact configuration of those. Those were used to pull logs down mountains. If the log slid down faster than the horse or mule pulling it, the hook would undo from the chain, so that the horse was not pulled down the mountain to its death.