From CreationWiki, the encyclopedia of creation science
A polystrate fossil is one that crosses more than one layer of stratified rock. Fossilized trees, for example, are frequently found in upright positions passing through two or more layers. These kinds of fossils offer clear evidence against a uniformitarian view of the earth's fossiliferous strata.
Numerous polystrate trees can be found in Yellowstone National Park, Joggins Nova Scotia, Sydney, Nova Scotia, Axel Heiberg Island in the Canadian high Arctic, and among the coal strata rocks of the United States (including Alaska), Germany, England and France. Normally these trees are found without roots attached, and in rare cases they will also have both roots and rootlets attached; however, even in these instances the trees are very likely not in situ (i.e. in their original places of growth) but rather have been transported by Floodwaters. Also, this strata has numerous rootlets that are buried individually (apart from being attached to a tree), which is further evidence of transport, as opposed to growth in situ. See references below for more information and documentation.