The Floating Mountains are huge chunks of rock that have broken off the barrier cliffs of the Serpent Mountain but rather than tumble to the grasslands below, they simply floated off and hover hundreds of feet above the ground.
Originally discovered by the gnomish mage, Abalard Manaspark in 823 KR , The key to their ability to float was not discovered until the year 865 KR and was not widely published or known widely. The Gnome Mage, Abalard Manaspark, that discovered the source of the mountains boyancy and was rewarded with one of Tor Gizad's highest honors. Abalard, not seeking riches or fame, returned to the Great Green Sea and claimed one of the floating mountains as his own to continue his research.
He knew that if word were to spread about the existence of the giant quartz-like crystals and their properties to levitate in the presence of ambient arcane energy - the world of wizards would not be the same again. It would increase the speed of air travel and change the world in which he lived.
That being said, Abalard could not resist his natural, Gnomish inclination to tinker with the large crystal points and see what he could do with them. Anything that could make a mountain float had to be useful somehow.
The many mountains and rocky fragments that float in clusters around each other make navigation and identification difficult. There are a few 'mountains' (large rocky peaks) that have been identified by Abalard in his map as well as a few 'sky islands' (which have large relatively flat areas).