438 HISTORICAL GEOLOGY 



REFERENCES FOR THE ORDOVICIAN PERIOD 



Blackwelder and Barrows, — Elements of Geology, pp. 339-348. 



Chamberlin and Salisbury, — Geology, Vol. 2, pp. 304-367. 



Grabau and Shimer, — North' American Index Fossils, Vols. 1 and 2. 



Schuchert, Chas., — P 'ale geography of North America: Bull. Geol. Soc. America, 



Vol. 20, 1910, pp. 485-489. 

 Scott, W. B., — An Introduction to Geology, pp. 560-577. 

 Ulrich, E. O., — Revision of the Paleozoic Systems: Bull. Geol. Soc. America, Vol. 22, 



191 1, pp. 281-680. 



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