Complex sentence: Many of the valleys in this region are sandy deserts, part of India's Thar Desert, with an occasional oasis of cultivation, but there are also some very fertile tracts; among these is the plain on which lies the town of Ajmer.
Split into simpler sentences: Many of the valleys in this region are sandy deserts, part of India's Thar Desert, with an occasional oasis of cultivation. Some fertile tracts are also present; among these is the plain on which lies the town of Ajmer.