CHAPTER XVI 



THE ORDOVICIAN PERIOD 



The system next younger than the Cambrian is the Ordovician. 1 

 The name Lower Silurian has been replaced by the above, although 



still occasionally used 

 by writers. 



Ordovician Physi- 

 cal Geography. 2 — In 

 North America dur- 

 ing this period the 

 epicontinental seas 

 (p. 405) varied greatly 

 in size and position 

 in the different stages 

 (Figs. 388, 389, 390, 

 391), shifting so often 

 and to such an ex- 

 tent that an attempt 

 to define their bor- 

 ders would require a 

 more extended de- 

 scription than seems 

 advisable. 



In general, it can 

 be said that the lands 

 about the epiconti- 

 nental seas were low 

 and that the seas 

 were shallow, as is 



rnc 



Fig. 38? mg W1 LIIC " >n of land and water in the 



l.ostence, and that tfL ' after Schuchert.) 



1 Or<i nota ' ) ly tm^truoblt^ name given because the rocks of the period arewell- 

 develo] 



•For 1 he physical geography of the different epochs of this and subsequent periods the 

 Btudenl is referred to ('has. Schuchert, — Paleo geography of North America, Bull. Geol. Soc. 

 America, Vol. 20, 1910, pp. 427-606, which contains the most accurate maps of these remote. 

 periods. 



418 



