Back in the days before boom trucks most loggers would build what they called a "brow" for loading logs. The brow was a kind of cribwork, usually built into a banking, that was raised so that is was level or just slightly higher than the bed of the truck or flatcar or trailer that was to be loaded with logs. The logs were hauled to the brow and rolled onto the truck from the brow. I have a picture of my grandfather standing on the brow taking a break from loading logs and i can remember seeing him loading logs onto a truck from the brow when I was a kid. It was right beside the road protruding out of the banking. Another way is to connect two long chains to the side of the flatcar and run the other ends under and around the log and then and over the car to the opposite side where they are hooked to a team of horses or tractor. when the horses move ahead the chains roll the log up the skids onto the car. Unhook, back up, set the chains on the ground, roll the next log onto the chains, repeat. I've seen that done using a logging sled to load logs in the woods.