SILURIAN AND DEVONIAN 277 



the discovery of other Silurian rocks in Siberia in the future which will 

 more closel}' connect the Silurian faunas of northeastern Europe and 

 Alaska. 



In this connection the known distribution of the peculiar brachiopod 

 Streptis greyi deserves consideration. It occurs in England, the island 

 of Gotland, Bohemia, Alaska, and Arkansas, while it is entirely unknown 

 east of the Mississippi river and in northeastern America. This pecu- 

 liarly developed species forms an important connecting link between the 

 faunas of Arkansas, Alaska, and Europe, and its apparent absence from 

 the eastern third of America points toward a northwestern rather than a 

 northern or northeastern connection between the Silurian faunas of 

 Europe and America. 



DEVONIAN 



Devonian terrains are known to be widely distributed in the Upper 

 Yukon basin, but their succession is but imperfectly determined. As 

 rocks of this period are well developed along the Yukon between Eagle 

 and Circle, and as their stratigraphic relations have been more closely 

 studied in this field than in any other part of the province, it will be well 

 to describe it in some detail. Some of the terrains here assigned to the 

 Devonian are included in Spurr's^^ "Eampart series." This fact has led 

 to a rather loose use of the term "Eampart series," and it has been made 

 to include all the Devonian of the Yukon region, especially where it con- 

 tains any greenstones. 



The Devonian probably includes a number of well defined stratigraphic 

 imits which will be referred to; these could not be differentiated on the 

 accompanying map because of lack of detailed information (see map, 

 page 278). First the geographical distribution of the Devonian in this 

 area will be considered (see map, figure 2), and then the stratigraphic 

 succession so far as it has been determined. Between Eagle and Calico 

 bluff there is a series of rocks, including drab shales, with some feld- 

 spathic sandstones and black slates and shale, which are assigned to the 

 Devonian. A second belt of rocks, which are probably Devonian, includ- 

 ing quartzites and limestones, with some cherts, outcrops a mile below 

 the mouth of Fourth of July creek (see map, figure 2), and continues 

 down the river for some 2 miles, to where it passes underneath the ]Meso- 

 zoic. The same belt probably extends westward and Avas observed again 

 on the lower part of Washington creek, where it is represented chiefly by 

 quartzites and tuffs. 



" J. E. Spun- : The geology of the Yukon gold district. Eighteenth Annual Report, 

 II. S. Geological Survey, part iii, pp. 155-168. 



I 



