Lord Vishnu took the Avatara of Hayagreeva, a white horse faced form, to rescue the Vedas stolen by the demons. Hence the Saligrama with typical horse mane like marks is Known as Hayagreeva Shila. Worship of Lord Hayagreeva is very auspicious for all types of knowledge and learning. It is also lord Hayagreeva who gave the two famous Devi Stotras – Lalita Sahasranama Stotra & Lalita Trishati stotras to Agastya Muni.