THE ORDOVICIAN PERIOD 



89 



America, thus implying a shallow sea connection between North 

 America and Europe. The scarcity of limestone in the European 

 Ordovician is in marked contrast with that of North America. 



In the British Isles, where the European Ordovician is thickest 

 (being many thousands of feet), great igneous intrusions and ex- 

 trusions took place, so that this region ranks as one of the greatest 

 ancient volcanic areas in Europe. 



Fig. 47 

 Sketch map showing the relations of land and water in Europe 

 during Ordovician time. Dotted area, water. (Slightly modi- 

 fied after De Lapparent.) 



As in North America, important geographic changes took place 

 toward the close of the period, and the Silurian often rests by 

 unconformity upon the Ordovician. In the British Isles the Ordo- 

 vician rocks were folded, upraised, and often metamorphosed, with 

 Silurian strata resting upon their eroded edges. 



Ordovician rocks are also known in Peru, Argentina, Australia, 

 Tasmania, New Zealand, Africa, India, eastern China, and north- 

 ern Siberia. 



