Them — The cedars; which being broken by the thunder, the parts of them are suddenly and violently hurled hither and thither. Sirion — An high mountain beyond Jordan joining to Lebanon. Lebanon and Sirion are said to skip or leap, both here, and Psalms 114:4, by a poetical hyperbole.
Related Commentaries of Psalms 29:6
Psalms 29:6
6 He maketh them also to skip like a calf; Lebanon and Sirion like a young unicorn.