Vishnupurana 2.4.40

2.4.40

yathoskakarmakartṛtvātsvādhikārokṣayāya te /
tatraiva taṃ kuśadvīpe brahmarūpaṃ janārdanam /
yajantaḥ kṣapayanty ugram adhikāraphalapradam //

The Surá sea is entirely encircled by Kuśa-dwípa, which is every way twice the size of the preceding continent. The king, Jyotishmat, had seven sons, Udbhida, Venumán, Swairatha, Lavana, Dhriti, Prabhákara, and Kapila, after whom the seven portions or Varshas of the island were called Udbhida, &c. There reside mankind along with Daityas and Dánavas, as well as with spirits of heaven and gods. The four castes, assiduously devoted to their respective duties, are termed Dámís, Śushmis, Snehas, and Mandehas, who, in order to be relieved of the obligations imposed upon them in the discharge of their several functions, worship Janárddana, in the form of Brahmá, and thus get rid of the unpleasant duties which lead to temporal rewards. The seven principal mountains in this Dwípa are named Vidruma, Hemaśaila, Dyutimán, Pushpaván, Kuśeśaya, Hari, and Mandara; and the seven rivers are Dhútapápá, Śiva, Pavitrá, Sammati, Vidyudambhá, Mahhvanyá, Sarvapápahará: besides these, there are numerous rivers and mountains of less importance. Kuśa-dwípa is so named from a clump of Kuśa grass (Poa) growing there. It is surrounded by the Ghrita sea (the sea of butter), of the same size as the continent.