More Info about the Silurian World      

	By middle Paleozoic time, approximately 400 million years ago, the Iapetus Ocean had closed bringing Laurentia      

and Baltica crashing together.  This continental collision, preceded in many places by the obduction of marginal island arcs,      

 resulted in the formation of the Caledonide mountains in Scandinavia, northern Great Britain and Greenland, and the       

Northern Appalachian mountains along the eastern seaboard of North America.      

	It is also likely that by middle Paleozoic times, North China and South China had rifted away from the Indo-Australian       

margin of Gondwana, and were headed northwards across the Paleo-Tethys Ocean. Throughout the Early and Middle       

Paleozoic, the expansive Panthalassic Ocean covered muchof the northern hemisphere.  Surrounding this ocean was a      

 subduction zone, much like the modern"ring-of-fire" that surrounds the Pacific Ocean.