Brahma Knowledge, by L. D. Barnett, , at sacred-texts.com
§ 2. The Four Vedas.—The hymns of the Ṛig-veda, composed by various authors some three thousand years ago, are almost the only monument of the first period of Indian thought; for the collections known as the Yajur-veda and
[paragraph continues] Sāma-veda are for the most part merely adaptations of the Ṛig-veda for special liturgical purposes, while the Atharva-veda, which was not admitted until much later into the Vedic canon, combines Ṛig-vedic hymns selected for ritual objects with a mass of various incantations of little or no philosophic and literary merit. The study of these hymn-collections in their liturgical application by the Brahman schools bore as fruit the bulky volumes known generically as Brāhmaṇas.