CAYUGAN SERIES

last of the three major divisions of Silurian rocks and time (the Silurian Period lasted from 438 to 408 million years ago). It was named for exposures studied in the region about Cayuga Lake, New York. During Cayugan time, marine waters on the North American continent became gradually restricted. Arid conditions prevailed, and evaporation produced many deposits of salt, gypsum, and anhydrite that are extensively mined. In New York and the Great Lakes region, Cayugan rocks are characterized by an extensive development of impure dolomites, these also being known as water limes. These rocks contain fossils of rather specialized fauna, the most familiar of which are the eurypteridslarge, aquatic, scorpion-like arthropods that probably preyed on worms and on the early fishlike vertebrates.