Danish Niels Steensen or Niels Stensen
born Jan. 10, 1638, Copenhagen, Den.
died Nov. 26, 1686, Schwerin, Prussia
Danish geologist and anatomist.
An eminent physician, in 1660 he discovered the parotid salivary duct (Stensen's duct). In his geologic observations, he was the first to realize that the Earth's crust contains a chronological history of geologic events that might be deciphered by careful study of rock strata and fossil s, which he identified as the remains of ancient living organisms. In 1669 he made the fundamental crystallographic discovery that all quartz crystals have the same angles between corresponding faces. He later abandoned science for religion and became a priest in 1675.