266 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



On the map the Silurian is not distinguished, being included in the unaltered and 

 probably also in the metamorphosed Paleozoic rocks. 



Q 5-6. YTJKON-TANANA REGION. 



The Fortymile group of crystalline limestone and quartzite with some graphitic 

 schist was provisionally correlated by Brooks ^"^^ with the Nome group and the 

 Skajit formation of northwestern Alaska. Later investigations by Brooks and 

 Kindle on Porcupine River have resulted in more definite determination of the 

 Silurian age of a massive limestone which may be equivalent to that of the Forty- 

 mile group. 



With regard to the Porcupine section, Brooks ^"^ says : " The Silurian is repre- 

 sented by at least 2,500 feet of magnesian limestone with some quartzites and 

 slates, which are probably conformable to the Ordovician. Its correlation with the 

 Fortymile series of Spurr is suggested but not proven." 



Kindle ^^^^ gives a list of 37 species collected from this limestone and comments : 



The Porcupine River fauna contains species which link it with the Silurian faunas of both 

 Europe and Araerica. Of these Rhynchotreta cuneata, Spirifer nobilis, and Pentamerus oblongus 

 have long been known in both European and American faunas. The peculiar little twisted 

 brachiopod Streptis greyi has been recognized at but one other American locality, however. 

 Williams has reported it from the St. Clair limestone fauna of Arkansas. In Europe it occurs 

 in the Silurian of Bohemia, in England, and at the island of Gotland. 



The Silurian fauna of the type represented by the species listed here is known to have a 

 wide distribution throughout the world. It is well known in various parts of Europe and has 

 been recognized in regions as remote as China, New Zealand, and Australia. This fauna occurs 

 in a magnesian limestone of considerable thickness — ^probably 2,000 feet. It is preceded in the 

 section by Ordovician limestones containing Maclureas. It is followed by a somewhat later 

 phase of the Silurian and by the Devonian. 



Q-E. 5. ENDICOTT RANGE. 



The Skajit formation of the Endicott Range, northern Alaska, consists of heavy- 

 bedded crystalline limestone and mica schist, in which a few obscm-e fossils, appar- 

 ently Silurian, were found by Schrader.™* 



T 16-17. ELLESMERE LAND. 



A thick section of Ordovician, Silurian, and Devonian strata occurs on the 

 north shore of Jones Sound, southern EUesmere Land, and has been described in 

 detail by Schei,^^"'* as follows: 



There are at Havnefjord, in Jones Sound, above some layers of quartz sandstone, which 

 entirely cover the gneiss granite there, a series of limestone conglomerates with marly schists 

 and pure limestones of a thickness of 1,200 to 1,500 feet. These are again overlain by a series 

 of beds at least 2,000 feet thick, of hard, impure limestones, brown or yellowish gray in color 

 and often remarkably heavy. 



At South Cape, which is entirely composed of this brown limestone, are found in the lower 

 parts Maclurea sp., and Halysites sp., referable to the Middle Silurian [probably Ordovician], 

 while west of it, at Bjorneborg, the upper parts of the series contaia badly preserved remaias 

 of Orthocerata, corals, and Pentamerus cfr. tenuistriatus. Hereafter the upper part of the 

 limestone seems to be equivalent to the older Upper Silurian (Landovery). This brown lime- 

 stone occurs from South Cape westward to Kobbebugten, in Hell Gate, and is broken at Lille 

 Sandor, tectonic disturbance bringing up the underlying conglomerate series and even the 

 Archean. * * * 



