DEVONIAN. 339 



can not be less than 3,000 feet and may be twice as great. The relation of the 

 Devonian to the Silurian is unknown, but is probably one of unconformity.^"^ 



The following notes on the Porcupine Valley are taken from a paper by Kindle i*^^ 



The lowest division of the Devonian is a hmestone formation about 325 feet in thickness. 

 It is a massive light-gray to blue hmestone weathering buff and considerably broken by joints. 

 It rests apparently unconformably on the graptohte shales described above and is followed in 

 the section by brown shale. The lower 5 feet of this shale may be seen resting directly on the 

 hmestone on the bank of the Salmontrout River just above its mouth. The total thickness of 

 this shale is unknown, but, judging from the covered slope extending upward from the hmestone 

 along the Salmontrout River, it prbbably amounts to several hundred feet. Outcrops of the 

 hmestone described occur on both banks of the Porcupine immediately above the Salmontrout 

 River, and it is proposed to call this formation the "Salmontrout hmestone," from the Salmon- 

 trout River, which is the nearest geographic feature having a name available for a formation 

 name. Fossils are abundant throughout this hmestone. Its strike and dip are concordant 

 with that of the subjacent Silurian shale and limestone and afford no evidence of deformation 

 at the close of Silurian sedimentation. 



Although no angular unconformity is shown in the relations of the Silurian and Devonian 

 series where observed, unconformable relations between the two are attested both by the hthol- 

 ogy and the faunas. In passing from the Silurian to the Devonian the hthologic change is an 

 abrupt transition from black shales to very pure limestones. The faunal change is from a Silu- 

 rian graptohte fauna to a Middle Devonian fauna, the Lower Devonian fauna being absent. The 

 Devonian hmestone forms a continuous outcropping chff 100 to 200 feet high for 1 mile above 

 the Salmontrout River, along the east bank of the Porcupine. It also outcrops on the opposite 

 side of the river in isolated exposures. 



Kindle gives a provisional list of 54 species preliminary to a full description of 

 the fauna and concludes : 



There are present in it several species which are either closely alhed to or identical with 

 species wliich first appear in the better-known American sections at a Middle or Upper Devonian 

 horizon. Since characteristic Lower Devonian species appear to be absent from the fauna, 

 its age seems to be either Middle or Upper Devonian. The list contains some species not 

 known below the Upper Devonian in the United States. One of the best known of these is 

 a variety of Pugnax pugnus, a species which ranges from the Rocky Mountains to New York 

 State and into the Mackenzie River district. Stropheodonta arcuata and S. calvini are also 

 known to have a wide distribution in the Upper Devonian. P. pugnus and S. arcuata first 

 appear in the New York section at the horizon of the Ithaca fauna. Associated with these 

 Upper Devonian forms we find several species characteristic of Middle Devonian horizons. 

 Among these are PholidostropJiia cf . iowensis, Cyrtina cf . Jiamiltonensis, ScJiucJiertella chemungensis 

 var. arctostriatus, Beticularia fimhriata, Nucleospira cf. concinna, and species resembling the 

 European forms Gypidula cf. hiplicatus and G. cf. galeatus. Two possible explanations of 

 this association of Middle and Upper Devonian species in the same fauna present themselves. 

 It has been shown by WUhams and Kindle that Middle Devonian species sometimes persist 

 tih late Devonian time and appear in certain New York sections associated with Upper Devonian 

 species. ° It appears most probable, however, from what we Imow of the relations of Pugnax 

 pugnus and its associated fauna to the Upper Devonian of New York, that the occurrence of 

 Upper and Middle Devonian species in the same fauna at Old Rampart is not the result of late 

 persistence of the earher fauna. This species evidently migrated into the New York province 

 from the northwest in Upper Devonian time. The two significant facts of its association 

 with Middle Devonian fossils in an Alaskan fauna and its abrupt appearance in an Upper 

 Devonian fauna in the United States, taken together, point very strongly to the probability 

 that intercommunication between the eastern Alaska province and the interior American 



a Am. Jour. Sci., 4th ser., vol. 13, 1902, p. 429. 



