Handbook of Paleontology 249 



tries the name Silurian is retained as defined by Mur- 

 chison. In America the name Champlainian for this 

 broad system is also used. This name, taken from 

 Lake Champlain (New York-Vermont) where most 

 of the formations now included under that term are 

 well developed, was proposed in 1842 by the geolo- 

 gists of the New York State Survey. 



Geology. As with the Cambrian so the Ordovician 

 rocks of Wales are strongly folded and much broken, 

 with numerous igneous intrusions and lava sheets. 

 The most typical representation of the Ordovician sys- 

 tem in Europe occurs in the Bohemian basin where 

 the rocks are richly fossiliferous and have been very 

 thoroughly studied. Nowhere in the world are the 

 Ordovician rocks preserved in such completeness and 

 with so little alteration as in North America, especi- 

 ally in the eastern section. Many of the formations 

 of this series are very fossiliferous and the fossils are 

 found beautifully preserved. The formations were 

 first studied in greatest detail in New York State which 

 is therefore regarded as the standard section and the 

 current names of the formations are those used in New 

 York. Other important localities in America are the 

 province of Ontario in Canada, the Upper Mississippi 

 Valley region, the Cincinnati and Nashville domes and 

 the Appalachian valley area. In the northern Appa- 

 lachian region the rocks which consist more often of 

 sandstones and shales have been intensely folded, as 

 seen in the Upper Hudson valley and slate belt coun- 

 try of New York and Vermont, and are similar in 

 appearance to the old rocks of Wales. In the Cor- 

 dilleran region also, rocks of this system are found 

 and have been traced into Arctic regions. 



