books 2 to 7 (usually referred to as the 'family books') … have been ordered according to the increasing number of hymns per book" ... "very importan… - Michael Witzel

During the Vedic period, there has been an almost complete Indo-Aryanization of the North Indian hydronomy. . . . Indo-Aryan influence, whether due to actual settlement, cultural expansion, or. ... the substitution of indigenous names by Sanskrit ones, was from early on powerful enough to replace the local names, in spite of the well-known conservatism of river names. The development is especially surprising in the area of the Indus civilization. One would expect, just as in the Near East or in Europe, a survival of older river names and adoption of them by the IA newcomers upon entering the territories of the people(s) of the Indus civilization and its successor cultures.... "such names tend to be very archaic in many parts of the world and they often reflect the languages spoken before the influx of later populations" (368-369). ... "by and large, only Sanskritic river names seem to survive" in the Northwest (370). [In the Kuruksetra area,] "all names are unique and new formations, mostly of IA coinage" (377). ...[in] "the 'homeland' of the Rgvedic Indians, the Northwest "we find "most Rgvedic river names . . . are Indo-Aryan, with the possible exception of the Kubha, Satrudri, and perhaps the Sindhu" (373). [These latter, according to Witzel (1999)] "prove a local non-IA substrate.

Since the SarasvatI, which dries up progressively after the mid 2nd millennium BC is still described as a mighty river in the Rigveda, the earliest hymns in the latter must have been composed by C.1500 BC. (p. 98)

"In Europe, river names were found to reflect the languages spoken before the influx of Indo-European speaking populations. They are thus older than c. 4500-2500 B.C. (depending on the date of the spread of Indo-European languages in various parts of Europe)... “in northern India rivers in general have early Sanskrit names from the Vedic period, and names derived from the daughter languages of Sanskrit later on" (WITZEL 1995a:104-105).