for your reading pleasure ...
http://www.uhh.hawaii.edu/~kenhon/GEOL205/flows/default.htm
See especially the “Lava Trees and Tree Moulds” section, wherein the following statement can be found “Lava trees and tree moulds are closely related phenomena. Both form when high volume surface flows engulf a forest. As shown in the sketch on the left, a flow initially surrounds the trunk of a tree and chills. This not only insulates the tree and prevents it from burning,...”
Cool, I wonder if those are 15 million years old too?