THE DEVONIAN PERIOD. 



421 



and Nova Scotia, and a remnant belonging to the same general prov- 

 ince occurs near Montreal; 1 (2) in the Appalachian belt, and (3) in 

 the lower Mississippi basin (see Fig. 191). 



During the Helderbergian epoch, as before, the sea of the Appa- 

 lachian trough seems to have had eastward, but not westward, con- 

 nections. The fauna of the Appalachian Helderbergian beds is very 

 similar to that of the region east of the lower St. Lawrence. From 



FiGo 192. — Helderberg limestone, Wilbur, New York. (Darton, U. S. Geol. Surv.) 



these relations it is inferred that the Helderbergian fauna of the eastern 

 coast, like the Silurian fauna of the same region, found entrance to 

 the Appalachian trough, and from relations which will not be detailed 

 here, it is conjectured that the entrance was effected by an inlet 

 near the present Chesapeake bay (Fig. 191). The fauna of the Helder- 

 bergian beds in the lower Mississippi basin is also of the Appalachian 

 type, indicating geographic conditions which allowed of the migration 

 of the Atlantic-coast faunas into this region. 



The Helderberg formation is largely limestone, which suggests 



1 Whiteaves, Am, Geol., Vol 24, 1899, pp. 210-40. A review of the Devonian 

 of Canada. 



