In 1958 Gauhati University granted doctorate to noted linguist Upendranath Goswami for his thesis 'A Study on Kamrupi: a dialect of Assamese', which later published as book in 1970 with same title. His research covers history, phonology, morphology and other peculiarities of ancient Kamrupi language; which now has lost its prestige and remained as dialect of one of its offspring's, the Assamese language. Find it here.
