Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 4
स चावनिज्यमानाङ्घ्रि: समन्तात् पयऊर्मिभि: ।करोति श्यामलां भूमिं हरिन्मरकताश्मभि: ॥ ४ ॥
sa cāvanijyamānāṅghriḥsamantāt paya-ūrmibhiḥkaroti śyāmalāṁ bhūmiṁharin-marakatāśmabhiḥ
The ground at the foot of the mountain is always washed by waves of milk that produce emeralds all around in the eight directions [north, south, east, west and the directions midway between them].
From Śrīmad-Bhāgavatam we understand that there are various oceans. Somewhere there is an ocean filled with milk, somewhere an ocean of liquor, an ocean of ghee, an ocean of oil, and an ocean of sweet water. Thus there are different varieties of oceans within this universe. The modern scientists, who have only limited experience, cannot defy these statements; they cannot give us full information about any planet, even the planet on which we live. From this verse, however, we can understand that if the valleys of some mountains are washed with milk, this produces emeralds. No one has the ability to imitate the activities of material nature as conducted by the Supreme Personality of Godhead.