South India, by contrast, remains in the Mesolithic stage until about 2500 BCE. In the 2nd millennium BCE, there may have been cultural contact between North and South India, even though South India skips a Bronze Age proper and enters the Iron Age from the Chalcolithic stage directly. In February 2006, a school teacher in the village of Sembian-Kandiyur in Tamil Nadu discovered a stone celt with an inscription estimated to be up to 3,500 years old. Indian epigraphist Iravatham Mahadevan postulated that the writing was in Indus script and called the find "the greatest archaeological discovery of a century in Tamil Nadu". Based on this evidence he goes on to suggest that the language used in the Indus Valley was of Dravidian origin. However, the absence of a Bronze Age in South India, contrasted with the knowledge of bronze making techniques in the Indus Valley cultures, questions the validity of this hypothesis.