Port Clarence Limestone, Alaska. 337 



Cambrian fauna has not previously been found in Alaska, its 

 occurrence here is of unusual interest. 



Areal distribution and general relations of the Port Clar- 

 ence. — A limestone series of considerable thickness, known as 

 the Port Clarence limestone, covers an extensive area in the 

 western part of the Seward Peninsula. This formation 

 includes the oldest rocks in the Peninsula whose age has been 

 determined by paleontologic evidence. It appears that meta- 

 morphisin has affected the area of the York Mountains in 

 which these rocks occur less than any other part of the Seward 

 Peninsula (see map fig. 1). As a result of the slight altera- 

 tions which they have suffered we have a more complete 

 knowledge of the faunas of these rocks than we have of any 

 other portion of the geologic column in the Seward Peninsula. 

 The type locality of the Port Clarence limestone is in the 

 western part of the Peninsula, in the York Mountains north of 

 Port Clarence harbor. Collier* applied the name to the lime- 

 stones from which the York Mountains have been carved. 

 According to Collier's original description, — 



" This formation comprises a thickness of at least 2,000 feet 

 of almost pure limestone. The basal beds are flaggy and 

 slightly schistose, but the strata become more massive in 

 ascending the series."f Collier's later provisional estimate 

 which gives this limestone series a thickness of " at least 5,000 

 feet":}: seems more likely to prove an underestimate than an 

 overestimate of their thickness. These limestones are in gen- 

 eral thin-bedded, as shown in figure 1, usually non-magnesian, 

 and are prevailingly bluish or dark gray in color. They 

 occupy an area of about 1,400 square miles in the York Moun- 

 tain region. On the west the limestones terminate abruptly 

 against a broad belt of argillites composed mainly of black slates 

 but including greenstones, sandstones and limestones, whose rela- 

 tive abundance is in about the order named. (See fig. 1.) Widely 

 divergent opinions have been held regarding the relationship 

 of the limestones and the argillite series by geologists who 

 have worked in this region. Brooks§ placed the slate or argil- 

 lite series below the limestone series which were later called 

 Port Clarence limestone. Hess|| considered the black shale 

 series to be probably younger than the Port Clarence. Collier^f 

 and Knopf** on the other hand agree that the slates are older 



*Prof. Paper U. S. Geo]. Survey, No. 2, p. 18, 1902. 



fOp. cit., p. 19. 



% Bull. U. S. Geol. Survey, No. 328, p. 73, 1908. 



55 Brook s and Shrader, Reconnaissance of the Cape Nome and Norton 

 Bay regions, Alaska, in 1900 ; A special publication of the U. S. Geol. Sur- 

 vey, p. 30. 1901. 



|| Bull. U. S. Geol. Survey, No. 284, p. 14, 1906. 



If Prof. Paper U. S. Geol. Survey, No. 2, p. 18, 1902. 



**Bull. IT. S. Geol. Survey, No. 358, pp. 12-13, 1908. 



