Digging in the dirt!

[stormdog]

This Summer I'll be doing four weeks of archaeology field school, which I assume will consist largely of working outside in the sun. I have a hat and will use sunscreen. But other than that, can you recommend fabrics that I should be looking for at thrift stores as I try to buy a few long-sleeved shirts for active outdoor work? Do I want cotton, linen, some kind of synthetic?

Thanks!