Treasures Hidden in the Sand (a reference to Deuteronomy 33:19) is a 19th-century thesis arguing for the possibility of discovering the source of tekhelet, a dye that the Bible instructs to use in the High Priest’s clothing, the tapestry in the Mishkan (Tabernacle), and tzitzit (fringes affixed to four-cornered garments). The Tosefta (Menachot 9:6) states that tekhelet comes from the secretion of a sea-creature called the chilazon, but the identity of the chilazon was lost since early medieval times and wearing tekhelet fell out of practice. “Treasures” addresses and refutes potential objections to a modern-day search for the chilazon, and describes the signs of the chilazon as described in rabbinic literature. It is considered an essential source on the topic.