Bhagavatapurana 5.1.32

5.1.32

_*
jambū-plakṣa-śālmali-kuśa-krauñca-śāka-puṣkara-saṃjñās teṣāṃ parimāṇaṃ pūrvasmāt pūrvasmād uttara uttaro yathā-saṅkhyaṃ dvi-guṇa-mānena bahiḥ samantata upakḷptāḥ //

Dwipas is separated by a sea and every Dwipa is in area double that of the one that is interior to it.

33. Of salt, juice, sugarcane, nectar, clarified butter, curd, milk and pure water are the seven seas which are the moats of the seven Dwipas and equal in extent to the Dwipas they severally enclose; every one of the seas in the given order is the outer boundary of the Dwipa enclosed by it; in those Dwipas Barhishmati's Lord appointed as rulers his dutiful sons, namely, Agnidhra, Idhmajihva, Yajnabahu, Hiranyaretas, Ghritaprishta, Medhatithi and Veetihotra: and in the said order they severally ruled their Dwipas.

31 & 32. The hollows (moats), wonderful as they are, caused by the tyres of the wheels of his chariot, became the seven seas and by those seas seven Dwipas of land are enclosed; they are called Plaksha, Salmali, Kusa, Krouncha, Saka, Jambu and Pushkara. Listen to my description of their dimensions. Every two of the