536 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



from the southern waters of the Atlantic, and many of these also find 

 their way into the northern waters of the Hudson sea. 



Saint Lawrence sea. — On the island of Anticosti, in the Gulf of Saint 

 Lawrence, there is a complete transition from the Cincinnatic into the 

 Siluric. The line of division between these two systems must here at 

 least ever be an arbitrary one, the determination of which is now being 

 worked out at Yale. On Anticosti the Siluric apparently terminates near 

 the base of the Eochester. Many of the species of this area are not only 

 European in aspect, but are also found in the Clinton formations of the 

 Appalachian trough. 



Another fine, even longer, but far less fossiliferous section is that of 

 Arisaig, Nova Scotia, recently restudied by Twenhofel 154 and the writer. 

 This succession of faunules, while clearly of European affinity, differs 

 markedly from all others of the Saint Lawrence sea, a condition probably 

 due in part to the rapid accumulation of muds and sands in this area, and 

 also to different sea ways. Farther to the northwest, in the Bay de Cha- 

 leur, at Black cape, near Eichmond and about Port Daniel, may be studied 

 other long sections of the Chaleur group, which continue the Anticosti 

 section certainly as high as the Guelph. Some of these fossils have been 

 described or listed by Billings. Near Dalhousie, and again about Gaspe, 

 may be seen the beds that continue into the Helderbergian, but unfortu- 

 nately they are almost unfossiliferous. 



Acadian trough. — Faunas similar to the foregoing, but far more sparse 

 in species, are also known in eastern Maine, buried in a vast mass of vol- 

 canic material said to attain a thickness of 46,000 feet. Among others, 

 here occur the two European guide fossils Conchidium hnigMi and Car- 

 diola interrupta. 



In folio 149, IT. S. Geological Survey, is described the Ames Knob for- 

 mation of Penobscot bay, Maine, which has a thickness of 580 feet. The 

 fauna was first listed by Beecher, and the list, somewhat changed, is re- 

 peated here. It contains Clinton forms in the lower half of the series, 

 while the upper portion has a fauna typical of the Eochester shale. Vol- 

 canic activity had begun in this area at this time, since two of the red 

 shale beds are composed of volcanic dust. 



Appalachian trough. — Very similar faunas are again seen in the Appa- 

 lachian trough extending from central K"ew York into Alabama. En- 

 trance from the Atlantic was effected in two places : in the north across 

 K"ew Jersey and in the south by way of the Gulf of Mexico into Alabama. 

 These biota are as yet very imperfectly known, but have been described in 



134 Twenhofel : American Journal of Science, vol. 28, 1909, pp. 143-164. 



