Rudolf Hoernlé in 1880 first proposed a binary grouping of Indo-Aryan languages, between an "outer" Magadhi-descended group containing Odia, Bengali, Eastern Hindi, and Marathi and an "inner" Sauraseni-descended group comprising Western Hindi, Punjabi, Sindhi, and Nepali. George Abraham Grierson further developed this theory into what is known as the Inner-outer hypothesis of Indo-Aryan languages, reassigning the Northwest zone (without Punjabi) to the Outer branch and further introducing a mediate sub-branch for Eastern Hindi. The grouping was postulated to be the result of two waves (by Hoernlé) or two periods (by Grierson) of the Indo-Aryan migration reflecting different dialect groups of Old Indo-Aryan. Masica lists some of the features that were seen as evidence for the separation: