Cob is a form of earthen building. Some of the first houses ever made were made out of cob. Medieval cob cottages are still standing in England. You can see cob sky scrapers in Yemeni. Cob structures (new and old) are all over the world. You know those old English cottages that are white with thatched roofs? Those are cob. You know those mud huts in Africa? Those are cob. You know those houses hobbits live in? You guessed it...cob! A cob mixture is made of clay, sand, straw, and water. The clay acts as the glue, the sand makes it strong, and the straw gives it it's tensile strength. You mix these ingredients together...usually with your feet on a tarp, and then sculpt your house with it. The word cob comes from an Old English root, meaning "a lump or rounded mass"[from The Hand Sculpted House]. After you mix the mud with your feet, you form it into round balls called cobs. The cobs are easy to transport and build with (you can throw them to each other). So that's how it got its name. You use these cob balls to construct/sculpt your house. It's kind of like adobe, but instead of making bricks first, you just sculpt your house with the wet mixture. In the end you have a monolithic structure that is thick, hard as concrete, and load-bearing. Pretty amazing stuff considering it's made out of nothing but readily available materials literally found in your own back yard. If you want to see some neat pictures of cob, I recommend clicking on the following link. You can select additional photo galleries on the menue to the left.
Or google image "cob cottage"...http://images.google.com/images?hl=en&q=cob+cottage&gbv=2