TERTIARY ROCKS, COLVILLE SERIES. 81 



area here discussed and Nulato, and include, in part at least, the so-called Nulato 

 sandstone. A description of this series was given in a previous report. a The fossils 

 on which the assignment is made were collected by the writer in 1899 in the 

 Nulato sandstone between Pickart's coal mine and Nulato, and are of interest as 

 being the first Upper Cretaceous fossils found in Alaska. Of this collection, Doctor 

 Stanton has reported the following forms, and refers the beds to about the same 

 horizon as the early Chico of the Pacific region in the United States: 



Upper Cretaceous fossils from the Yukon Basin. 

 Ostreo. 



A norma. 



Mytilus. 



Cardiuia. 



Opis? 



Lucina. 



Trigonia cf.T. leana Gabb. 



Corbula. 



Actaeonella cf. A. oviformis Gabb. 



East of the international boundary both Upper and Lower Cretaceous fossils 

 have been found on the Porcupine bj r Mr. R. G. MeConuell, of the Canadian geo- 

 logical survey. 6 



TERTIARY ROCKS. 



COLVILLE SERIES (oLIGOCENE AND PLIOCENE). 



Character and occurrence. — The Colville series is named from the large river 

 along which it occurs and is excellently exposed. It is a series of Tertiary terranes 

 which underlies the flat tundra country, or Arctic Coastal Plain, that succeeds the 

 more southerly rolling plain formed by the Upper Cretaceous or Nanushuk series, 

 which it apparently unconformably overlies, being itself in turn unconformably 

 overlain by the Gubik sands. The strata which have been thus grouped extend 

 along the Colville from some distance above the mouth of the Anaktuvuk nearly 

 to the Arctic coast, occupying a belt 80 to 100 miles wide. Judging from tha 

 topography, the series probably has a very considerable extent in an east-west 

 direction, possibly reaching the northwestern coast in the region of Point Barrow 

 and farther southward. It also appears along the northern coast in places between 

 Point Barrow and the mouth of the Colville, but has not been recognized. 



The inland edge of the coastal plain, formed essentially by this series, has an 

 elevation of about 800 feet, from which, with very gradual slope, the surface descends 

 approximately to sea level at the coast. Beyond this, the very gradually deepening 



aScnrader, F. C, Reconnaissance along the Chandlar and Koyukuk rivers, Alaska : Twenty-first Ann. Rept. TJ. S. 

 Geol. Surrey, pt. 2, 1900. 



b Ann. Rept. Geol. and Nat. History Survey of Canada, vol. 4, 1888-1889, Montreal, 1890, pp. 122-125 D, 



189— No. 20—04 6 



