Shaligramas are mostly black coloured stones with marks, and are the fossilized remains of now extinct sea dwelling ammonites. Hence they are found in river beds and other regions that were once underwater, the most popular being the Himalayas and Nepal. Historically, the use of Shaligrama (or Salagrama) Shilas in worship can be traced to the time of Adi Shankara through the latter's works. Specifically, his commentary to the verse 1.6.1 in Taittiriya Upanishad and his commentary to the verse 1.3.14 of the Brahma Sutras suggest that the use of Saligrama in the worship of Vishnu has been a well-known Hindu practice. A good number of false shaligrams too remain in circulation. Since they were underwater, the belief that these creatures only ate tulsi leaves is a myth.