twenhofel: expedition to the Baltic provinces. 311 



17. Isotelus robustus. 



18. Platylichas cicatricosus. 



19. Proetus ramisulcatus. 



Stratigr.\phic and Faunal Relations of the Borkholm Forma- 

 tion TO the Lyckholm. 



There are no reasons for believing that the Borkhohn is other than 

 conformable on the Lyckholm and directly continuous thereto. 

 Furthermore, the faunas are essentially identical and at least fifty- 

 three of the ninety-five Borkholm species occur in the Lyckholm. 

 Several of these common species belong to the genus Halysites. I 

 believe it will ultimately be found necessary to unite several of these; 

 but this will not change the strong faunal similarity. Each formation 

 contains many species of Silurian aspect; this is shown to a greater 

 degree in the Borkholm, where Silurian forms are conspicuous and 

 abundant, but the Ordovician expression dominates. 



Time Equivalents of the Lyckholm and Borkholm. 



At present these can be given in only a general way. When the 

 collections have been secured and submitted to a careful study it is 

 hoped to give a detailed correlation. 



Considered as a whole the faunas bear an aspect not generally fami- 

 liar to American stratigraphers. The large Porambonites ; the asso- 

 ciation of Halysites and meml^ers of the Heliolitidae with large 

 Hormotomas, Maclureas, and Subulites; and the abundance of large 

 Triplecias are faunal groupings not occurring in America, yet certain 

 associations are similar and the faunas have many components which 

 are present in American deposits, the wTiter being constantly im- 

 pressed with certain striking similarities. 



The points of contact with American sections are greatest in num- 

 ber in the Anticosti formations,^ where the facies and faunal associa- 



1 The Anticosti section is, figuratively speaking, on the frontier of the American Upper 

 Ordovician and Silurian, and hence would be most likely to show the greatest faunal similari- 

 ties to the strata of like age of northwestern Europe. The Anticosti section consists of eight 

 formations of which the lower four are Ordovician and the upper four Silurian. Named from 

 the summit downward, the formations are as follows. 



Silurian Chicotte. Ordovician Ellis Bay 



1223 feet Jupiter River. 939 feet. Charleton 



Gun River. English Head 



Becsie River. Macasty. 



