Matsya Purana — Kailasa
तेषां तु दृश्यते चन्द्रे शुक्ले कृष्णे समाप्लुतिः ते भारतस्य वर्षस्य भेदा येन प्रकीर्तिताः //
teṣāṃ tu dṛśyate candre śukle kṛṣṇe samāplutiḥ te bhāratasya varṣasya bhedā yena prakīrtitāḥ //
In their case, a convergence is observed in the Moon, through the bright fortnight and the dark fortnight. It is by this lunar basis that the divisions of Bhārata-varṣa have been set forth.
This verse is not describing Pralaya; it highlights lunar reckoning (bright and dark fortnights) as a framework used to explain or align the divisions of Bhārata-varṣa.
By grounding divisions and distinctions in lunar cycles, it supports dharmic timekeeping—choosing proper tithis/fortnights for governance, taxation cycles, festivals, vows, and household rites aligned to śukla and kṛṣṇa pakṣas.
The ritual takeaway is calendrical: many temple consecrations, vratas, and śrāddha-related observances are scheduled by śukla/kṛṣṇa pakṣa; the verse underscores the Moon-based basis for such liturgical timing rather than giving a specific Vāstu rule.