Port Clarence Limestone, Alaska. 349 



lum from Cape Lisburne fauna which is known to be of Car- 

 boniferous age. The former species is common to the Devil 

 Mountain and Harris Creek localities. The most abundant 

 fossil in the Harris Creek and Baldy Mountain localities is an 

 undetermined species of Striatopora. Thus the three localities 

 appear to represent a single horizon. This horizon is either 

 of Devonian or Carboniferous age, in the writer's opinion. It 

 certainly has much closer affinities with the Carboniferous 

 fauna at Cape Lisburne* than it has with any fauna known 

 in the Port Clarence limestone. The limestone at Baldy and 

 Devil Mountains should, it is believed, be correlated with the 

 limestone at Cape Mountain which has been referred to the 

 Carboniferous on satisfactory evidence. f 



Summary. — It has been shown in the preceding pages that 

 the rocks which have been mapped as Port Clarence limestone 

 range from Upper Cambrian to Devonian or Carboniferous. 

 The older of these Paleozoic rocks, including the Cambrian 

 and Ordovician beds, occur in the type region of the Port 

 Clarence, in a limestone series which is not known to have any 

 stratigraphic break. The middle Paleozoic faunas which have 

 been included in this limestone as it has been mapped are 

 known only from occurrences outside the type region. One 

 of these, a fauna of late Silurian age, is found in a limestone 

 of very different lithologic type from any known in the type 

 region of the Port Clarence, which clearly represents a forma- 

 tion distinct from either that holding the Ordovician on the 

 one hand, or the Devonian or Carboniferous faunas on the 

 other. 



It appears probable from the data which has been presented 

 that in the more detailed work of the future the term Port 

 Clarence limestone will have to be restricted to beds character- 

 ized by one or more of the pre-Silurian faunas noted in this 

 paper. There is however not sufficient information available 

 concerning the range of these faunas and the stratigraphic 

 relations of the beds holding them to justify a redefinition of 

 the formation at present. 



* Bull. IT. S. Geol. Survey No. 278, pp. 22-28, 1906. 

 + Bull. U. S. Geol. Survey No. 328, pp. 81-82, 1908. 



