Petriﬁcation occurs when minerals, usually silica, replace the cellulose of a tree. The result is a mineral log that preserves many details of the original log, even the rings. Postglacial petriﬁed forests are common in the estuaries of the American Southwest. The largest known petriﬁed forest is to be found in (and the term in North America almost always brings to mind) Petriﬁed Forest National Park in Arizona, adjoining the Navajo Indian Reservation. In over ninety-ﬁve acres, six separate “forests” display jasper and agate logs lying on the ground surrounded by variegated colors of ancient chips and fragments. These “stone trees” died and fell by natural processes, such as ﬁre or fungus or even insect infestation. Buried in mud and sand that contained substances such as silica-rich volcanic ash or salts rich in uranium, groundwater carried minerals into the logs, replacing the wood cells and eventually resulting in striking statuary forms. Prehistoric North American peoples lived among these trees, and ruins of their dwellings remain. The adjective petriﬁed means changed into stone or a stony substance. Figuratively, petriﬁed suggests being startled or terriﬁed, or being paralyzed with fear.