Jigsaw - Douglas  Smith Nice little kids' scifi story, illustrating the theory of tectonic plates - read it as a freebie from amazon on my Kindle. It passed the time on one of my daily commutes very well. The background notion of an advanced and extremely ancient civilization (the "wormers") who may or may not be encouraging mankind into deep-space exploration, is quite intriguing - perhaps it is a feature of the author's universe for which this free story is likely a teaser?