Dan Mouer, as usual, makes an excellent point. Tar pits look like chacoal pits, but in northern hardwood forests, there were similar kilns for roasting chemicals, too. In fact, the latter days of charcoal foundry fuels in PA were fueled, if I may make a pun, by hardwood charcoal byproduct of these kilns. So hardwood forests might also have "charcoal" pits that were not really primary charcoal, but charcoal as a byproduct, kilns.