What Are Some Other Useful Proxies for Economic Health and Economic Activity?

In many parts of europe there isn't much stone, you need bricks. Amean brick is the most effective of building material. You can make a roof with wooden shingles which are just wood and tiles - but it's nothing like as durable as a tiled roof. The amount of money you make from a brick or a tile is really very small in comparison to the effort of moving it. Those industries just disappear.