Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 45: The Churning of the Milk Ocean
Text 1.45.2

अत्यद्भुतमिदं ब्रह्मन्कथितं परमं त्वया।
गङ्गावतरणं पुण्यं सागरस्यापि पूरणम्॥

atyadbhutam idaṁ brahman kathitaṁ paramaṁ tvayā
gaṅgāvataraṇaṁ
puṇyaṁ sāgarasyāpi pūraṇam

atyadbhutam = amazing; idam = this; brahman = O brāhmaṇa; kathitam = as described; paramam = is extremely; tvayā = by you; gaṅgā-avataraṇam = narration of how Gaṅgā descended; puṇyam = auspicious; sāgarasya = the ocean; api = and; pūraṇam = how was formed.

O brāhmaṇa, this auspicious narration of how Gaṅgā descended and how the ocean was formed is extremely amazing.

The ocean was formed when the sons of Sagara dug the earth.