Bhagvat Puran Skandh 4 Adhyay 18

Earth who has taken the shape of a cow explains to Maharaj Pruthu why she is hiding the different types of fauna, flora and other good things. She requests that Maharaj Pruthu finds the right calf and the right shepherd to milch this cow and also provide flat lands to people by demolishing some of the hills. Following that mother Earth provides what is required by different types of beings. Maharaj Pruthu who has taken the Earth under his refuge, makes her his daughter.