346 E. M. Kindle — Faunal Succession in the 



Pelkcypoda : 



Ctenodonta cf. levata Hall. 

 Cyrtodonta sp. unclose. 



Gastropoda : 



Liospira sp. undet. 



Lophospira quadrisidcata ? U <fc. S. 



" sp. undet. 



Trochonema cf. umbilicatum Hall. 



Other beds holding the same fauna as 13b follow it in the 

 section. These, together with the limestones included in beds 

 13a and 13b, appear to give the limestones holding the fauna 

 listed from 13a and 13b a thickness of about 500 feet. A 

 considerable thickness of limestones follows these fossiliferous 

 beds along the Don River in which no organic remains were 

 found. These may represent the Silurian limestones. The 

 series of limestones holding the fauna of stations 13a and 

 13b are somewhat darker in color than the Cambrian and 

 Lower Ordovician limestones. Bands of very dark limestones 

 and of magnesium limestone interpolated in the gray lime- 

 stones are more common in this than in the lower series. No 

 stratigraphic break has been observed anywhere in the Port 

 Clarence limestone, but it is probable that one or more such 

 breaks are present. 



Although recognizing the strong affinities between the 

 faunules from stations 13a and 13b, Mr. Ulrich is inclined to 

 consider the former to be the equivalent of the Black River 

 fauna, and the latter (13b) to represent the Richmond fauna. 

 The completely exposed section between the two faunas, how- 

 ever, appears to afford no evidence of any stratigraphic break 

 which the definite correlation with these two Ordovician hori- 

 zons would suggest. 



The facts which do not appear to be open to question or dis- 

 cussion regarding the faunas from stations 13a and b are that (1) 

 they are distinctly younger than the trilobite fauna from station 

 6 at the mouth of Lost River, and (2) they are of Middle or 

 Upper Ordovician age. The older of these faunas, 13a, appear 

 to represent about the same general horizon of the Ordovician 

 as the fauna of this age discovered by the writer in the Porcu- 

 pine River in northeastern Alaska.* Still another and later 

 fauna than any of those already noticed was found by Collier 

 in or near the typical region of the Port Clarence limestone 

 in beds ascribed to that formation. This locality was not revis- 

 ited by the writer, hence the list of species determined by 

 Schuchert from Collier's collection will be quoted. 



*Kmdle, E. M., Geologic Reconnaissance of the Porcupine Valley, 

 Alaska ; Bull. Geol. Soc. America, vol. xix, p. 323, 1908. 



