276 BROOKS AKD KIXDLE PALEOZOIC EOCKS OF UPPER YUKOX 



Meek/' Etheridge/^ and Emerson.*'^ The recent explorations of Low"'' 

 and Schei'^ have added to onr knowledge of these northeastern faunas. 

 The several paj)ers 1)}' these authors show that a large percentage of the 

 species of this northeastern American Arctic fauna is common to the Mid- 

 dle Silurian of Europe and the interior of America, with which the Alas- 

 kan fauna is affiliated. 



Whether the Silurian fauna of the Mississippi valley, Canada, and 

 Arctic America received its foreign element via a northeastern or a north- 

 western route can not perhaps be conclusively determined with our present 

 knowledge, but some of the considerations which seem to point to the 

 latter conclusion may be stated briefly. 



To the northeast of the north Greenland Silurian" the nearest Icnown 

 Paleozoic rocks are those of Spitzbergen; but these do not include the 

 Silurian, so far as known. Moreover, a marine trough showing depths of 

 from 10,000 to 15,000 feet separates the land masses of Greenland and 

 Spitzbergen. Turning to northwestern America, we find in sharp con- 

 trast with this a continuous continental shelf connecting the Alaskan, 

 Asiatic, and European Coasts. The theory of the relative fisity of the 

 great marine troughs lends probability to the supposition of littoral con- 

 ditions having existed during the Silurian in the general region of the 

 Alaskan and Siberian coasts. On the other hand, the comparatively great 

 depth of the sea to the northeast of Greenland makes unlikely the exist- 

 ence of a shoreline across it during the Silurian, which would have been 

 required for trans-Atlantic migration of faunas in that region. 



But little is known of the Silurian fauna of Siberia. Silurian rocks 

 are reported to occur, however, in the new Siberian islands and in the 

 Upper Yenisei Eiver valley.'^ 



These occurrences of the Silurian in Siberia, in the intermediate region 

 between the Silurian sections of the Urals and Alaska, leads us to expect 



=° Arctic Silurian fossils. Appendix, p. ccvii, to Journal of a voyage in BafBns bay 

 and Barron straits in the years 1850-51, etc., by P. C. Soutberland. London, 1852. 



^ Geological account of the Arctic archipelago. Appendix IV to A narrative of the 

 discovery of the fate of Sir John Franklin, etc., by Captain M'Clintock. Berlin, 1860, pp. 

 341-372, with map. 



"^ Preliminary notice of a small collection of fossils found by Doctor Hays on the west 

 shore of Kenneday channel. American Journal of Science, second series, vol. 40, p. 31. 



^^ Palajontology of the coasts of the Arctic lands visited by the late British expedition 

 under Captain Sir George Nares. Quarterly Journal of the Geological Society of Lon- 

 don, vol. 34, pp. 568-639, pis. 25-29. 



"8 On the geologj' of Frobislier bay and Field bay. Appendix III to Narrative of the 

 second Arctic expedition made by C. F. Hall. Washington, 1879. 



"> New Land. Four years in the Arctic regions, by Captain Otto Sverdrup, with geo- 

 logical appendix to vol. ii by P. Schei, 1904, pp. 456-458. 



"i The cruise of the Xeptiine. Report on the Dominion government expedition to 

 Hudson bay and the Arctic islands, by A. P. Low, Ottawa, 1906, pp. 322-336. 



'2 Ed. Suess : La face de la terre, tome iii, 1902, pp. 24-52. 



