SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Leonardo studied the stratification of rocks and the flow of water. He concluded that "the stratified stones of the mountains are the layers of clay deposited one above the other by the various floods of the rivers.". He speculated that fossils are the preserved remains of dead life forms. He observed that distinct layers of rocks and fossils were formed at different times. Fossil shells in Lombardy led him to conclude that massive geophysical forces had raised land once covered by sea. He realised that the oldest rocks are at the base of the sequence.
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