Cool vintage tractor picture
Probably not a Caterpillar, but a very interesting use of tracks:
Link via BoingBoing.
What is that contraption, anyway? Seems there’s a popular tourist destination off the British coast called Burgh Island. You have to cross a narrow sand isthmus to get there, but at high tide the isthmus is under water. So, a ferry was invented to take people there without soaking their pant legs. The picture above is from 1936. An updated version of the ferry is still in use (with fat tires instead of tracks).