That which is the unmanifest ultimate cause becomes manifest as Śiva, free from ailment. When that becomes dichotomised, Brahma is born of that in due course.
पातालानि तु सप्तैव भुवनानि तथोर्द्ध्वतः ।। उच्छ्रायो द्विगुणस्तस्य जलमध्ये स्थितस्य च ।। १० ।।
The nether worlds (pātāla) are seven only. The upper worlds are also seven (bhuvana). The height of the universe is twice as such and it stands in the middle of water.