Matsya Purana — Cosmography of Jambūdvīpa: Varṣas
पर्वतप्रभवाभिश्च नदीभिस्तु समन्ततः प्रागायता महापार्श्वाः षडिमे वर्षपर्वताः //
parvataprabhavābhiśca nadībhistu samantataḥ prāgāyatā mahāpārśvāḥ ṣaḍime varṣaparvatāḥ //
Encircled on every side by rivers born of the mountains, these six Varṣa-mountains stretch eastward and possess vast flanks.
This verse is not about Pralaya; it describes cosmic geography—how regional mountains (varṣa-parvatas) are bordered by river systems originating in mountains.
Indirectly, it frames the Purāṇic worldview in which kingship includes understanding and protecting the land—mountains and rivers as natural boundaries, resources, and sacred features to be honored and safeguarded.
No direct Vāstu rule is stated, but the emphasis on mountains and rivers as defining, life-giving features aligns with Vāstu and ritual preferences for auspicious water sources and stable natural boundaries when selecting sacred sites.