i >usn\ 



found to have been :ed at the stage when they 



her in the interior, but all must have had 

 during which then .ving and advancing upon the continent 



along their particular lines of invasion. As each in succession 



through the coalescence of the ing gulf- 



with the fauna that had previously invaded the region, tha 

 commingling and conflict of the various assemb. ■ - ulting in the 



elimination of so:.. ies and the adjustment of others to one another. 



Tne resu> f the forms surviving from th mas, 



and th ment -. : una. In thi- 



or the other of the faun; isually dominant and gave the chief 



character:- . s tc the new fauna. 



The originating tracts of the invading faunas. — The places of origin 

 of these faunas cannot be le&ernrine present with certainty, but 



the following are the suggestions of present evidence, and m 



r£±Lg hypotheses until fuller data shall establish permanent 

 interpretations. Of the Helderberg fauna, the more local elements 

 probably originated in the great embayment at the mouth of th 

 Lawrence and on the border of the adjacent continental shelf. The 

 lese element seenae to fa an derived from the coast border 



of the \ North Atlantic, which seems to have connected the Ameri- 

 can contii- :.: with southern Europe, but not directly with 

 7.7 Hereyman fauna which characterizes thk 

 jian in southern Europe has much in common with the Helder- 

 berg fauna of America, while both were markedly different from 

 . - Devonian fauna of northern Europe and northern . 

 . ■ ugh a fauna of Helderbergian aspect has fc t one 



locality in the far northern islands. 1 



^nce here to the loc American phase, it i 

 I that in the St. Lawrence embayment the strata show gradual 

 passage from the Silurian fauna up into the Helderberg fauna. It 

 will be recalled that the St. Lawrei- was a harbor of 



refuge for the Ordovician life when it was forced to retire and undergo 

 transition into the Silurian type. History seems to have acquired 

 the habr ting itself thus The Helderberg fauna seems 



to have advanced from the - . _~ion of the Midd 



into the A palac hi an valley trough, and to L: ad wes* 



1 Meek, Am. Jour 3ri . XL, p. 31. 



