William Scott Shelley 
Soma and the Indo-European Priesthood [EPUB ebook] 

This work traces the origins of religion to the "Agricultural Revolution" and is the first to do so. Through the ancient Vedic literature, the archaeological record, and through chemistry, the author identifies how early Indo-Europeans produced the Soma of the Rig-Veda, Haoma, and the Greek Kykeon, the center of the Greek Eleusinian Mysteries.