Port Clarence Limestone, Alaska. 347 



" Loc. 3 AC146 (near the forks of Rock Creek, a northern tribu- 

 tary of Agiapuk River) has 



Stromatopora sp. 



Favosites favosus Gold fuss. 



Favosites cfr. niagarensis Hall or F. gothlandicus Fought. 



Columnaria ? apparently closely related to Favistella 



reticulata Salter of the Arctic Silurian. 

 Halysites catemdaria feildeni Etheridge. 

 Halt/sites catemdaria harti Etheridge. 

 Diphyphyllnm cfr. rmdticaulis (Hall). 

 Alveolites sp. 



Gasteropods, one a Lophospira, another a Hormotoma. 



Orthoceras sp. undeterminable." 



This fauna as determined by Prof. Schuchert appears pretty 

 clearly to represent the middle Silurian. Larger collections of 

 it will probably show that it is the equivalent of the middle 

 Silurian* fauna on the Porcupine River in northern Alaska. 



A late Silurian fauna, comparable with the Guelph, occurs 

 in a limestone which has been correlated with the Port Clar- 

 ence fauna, but which is unknown in the type region of the 

 Port Clarence. It was originally discovered by Mendenhall at 

 White Mountain on the Fish River. When this fauna was 

 first discovered the rich and excellently preserved fauna from 

 Glacier Bay in southeastern Alaska was unknown and unavail- 

 able for comparison with it, and the few cross-sections of large 

 lamellibranchs representing the first collection were provision- 

 ally referred to the Mesozoic or Tertiary.f Since the south- 

 eastern Alaska fauna has become available for comparison 

 there ceases to be any question as to the error of the earlier 

 opinion. Through identity with the Glacier Bay and Fresh- 

 water Bay fauna:}: it is well established that the White Moun- 

 tain fauna is of late Silurian age. Several hundred feet of 

 white to light gray magnesian limestone forms an eminence 

 known as White Mountain which rises 300 feet or more above 

 the broad alluvial plain of the Fish River. The limestone is 

 much broken by joints and shows very indistinct bedding 

 plains. Freshly broken specimens emit a strong fetid odor. 

 The thickness can only be conjectured. The limestone at 

 White Mountain contains in certain strata numerous specimens 

 of a large, thick-shelled pelecypod which is identical with a 

 species occurring in southeastern Alaska — abundantly at Glacier 

 and Freshwater Bays in association with other late Silurian 



*Op. cit., p. 325. 



f Mendenhall, W. C, A reconnaissance in the Norton Bay region, Alaska, 

 in 1900, p. 204, in Eeconnaissances in the Cape Nome and Norton Bay 

 regions, Alaska, in 1900 ; U. S. Geol. Survey, 1900. 



X Brooks, A. H., Prof. Paper, U. S. Geol. Survey, No. 1, p. 19, 1902. 

 Kindle, E. M., Jour. Geology, vol. xv, p. 323, 1907. 



