Honey, What's a "Skolithos"?

In my travels throughout the Park, I'll sometimes hear a reference to the geology of the areas I'm visiting - I've even posted on that topic from time to time when I learn something new.  I'd often heard about this variety of "trace fossil" - the skolithos, and finally had a chance during the Wildcat/RipRap hike to learn how to identify them.

Referring to the website for Shenandoah National Park, there is a good article on Park geology at this link:
http://www.nps.gov/shen/naturescience/chilhowee.htm.  Quoting from that, here is the reference to skolithos:

"...the one observable fossil can be seen in the Erwin Formation, a preserved worm burrow known as skolithos, which appears as long, straight tubes within the white quartzite."

The quartzite, shown in the two photos, is a sedimentary rock that dates from 500 million years ago, an era  before any of Earth's complex life forms had appeared.  Wikipedia (search on skolithos) goes on to describe this particular type of fossil as being "usually associated with high-energy environments close to the shoreline."

As we walked through these areas, Dan mentioned that we were walking along an ancient beach, adding to the adventure of that day's hike.