Shadows of the Heart
Earth Pony magic, unlike Unicorn magic, is a subtle magic. It will never have the flashiness that pegasus magic has. However, like an Earth Pony, this subtle magic can always be depended on to help out the Earth Pony in almost any situation…combat, or otherwise.
It should be noted that several structures that exist today wouldn’t have been possible without Earth Ponies. The SPP towers, for instance, while commissioned by Rainbow Dash and her ministry, were built by Earth Ponies. The various Ministry Buildings, pipbucks, terminals, and even weapons were all built by Earth Ponies.
Earth Pony magic is magic that causes an object built by an Earth Pony to stand the test of time, to whether the ages. It may not be flashy… but it gets the job done.