Can this god, 'most august of Vedic deities,' as Bergaigne and others have called him, have belonged as such to the earliest stratum of Aryan belief?
There are some twelve hymns in the Rig Veda in Varuna's honor.

Of these, one in the tenth book celebrates Indra as opposed to Varuna, and generally it is considered late, in virtue of its content.

Of the hymns in the eighth book the second appears to be a later imitation of the first, and the first appears, from several indications, to be of comparatively recent origin.[72] In the seventh book (vii.

86-89) the short final hymn contains a distinctly late trait in invoking Varuna to cure dropsy; the one preceding this is _in majorem gloriam_ of the poet Vasistha, fitly following the one that appears to be as new, where not only the mysticism but the juggling with "thrice-seven," shows the character of the hymn to be recent.[73] In the first hymn of this book the late doctrine of inherited sin stands prominently forth (vii.86.

5) as an indication of the time in which it was composed.
The fourth and sixth books have no separate hymns to Varuna.