On which the lichens grow

"Many New England stone fences built between 1700 and 1875 were laid by gangs of workers who piled stone at the rate of so much a rod. Edwin Way Teale says that in the latter years of the past century, before economic and social developments began obliterating some of the walls, there were a hundred thousand miles of stone fences in New England. Even today, for many of them, the only change has been the size of the lichens, those delicate rock-eating algae that can live nine hundred years."

— William Least Heat Moon, in Blue Highways