Matsya Purana — The Rite and Glory of Meru-Dāna: The Tenfold ‘Gift of Meru’ and Mountain-Offe...
धान्यद्रोणसहस्रेण भवेद्गिरिरिहोत्तमः मध्यमः पञ्चशतिकः कनिष्ठः स्यात् त्रिभिः शतैः //
dhānyadroṇasahasreṇa bhavedgiririhottamaḥ madhyamaḥ pañcaśatikaḥ kaniṣṭhaḥ syāt tribhiḥ śataiḥ //
Here, a mountain-like heap of grain is deemed best when it amounts to a thousand droṇas; a middling one is five hundred; and the least is three hundred (droṇas).
This verse does not discuss pralaya; it classifies the sizes of grain-donations (dhānya-dāna) using the droṇa measure and ranks them as best, middling, and least.
It provides a practical dharma guideline: householders (and kings as chief patrons) should perform charity with clear standards—here, specifying graded quantities of grain for meritorious giving.
The significance is ritual and administrative: it standardizes donation amounts (in droṇas) for a prescribed offering of grain, helping ensure consistent, auditable religious gifts rather than temple-architecture rules.