When flowing lava on the surface engulfs trees, the lava may cool before the tree has completely burned away, and leave an imprint of the tree in the lava. Basically this is a type of fossil known as a cast. Tree molds are more commonly found within surface lava flows, but occasionally they are seen underground as in the example below. There are also lava tree mold caves, which consist entirely of tree molds which may connect together. One such is a public-access cave in Mount Saint Helens National Monument, near Ape Cave.