206 ECONOMIC GEOLOGY 
drifted into the lagoons or grew in them, give rise to oi] 
on distillation. Oil shales are known in many parts of the 
world ; they include the Ordovician shales of Esthonia; De- 
vonian shales of the Eastern States of America ; Lower 
Carboniferous in Scotland ; Upper Carboniferous or Permian 
in New South Wales, Tasmania, South Africa, and France. 
There are vast deposits of Cretaceous and Eocene age in the 
Rocky Mountains, especially in Colorado and Utah, and large 
deposits of rich Pliocene oil shale at Mepale in South-eastern 
Burma.