76 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



traversed by a subordinate or minor system of cross folds <>r warnings, with axes 

 trending north and south. <^i \"Lny: rise to occasional low domes, a> shown in fig. 3 

 (p. 46), which also shows that the region has been subjected to considerable denudation. 



The series is freely traversed by two systems of jointing, as shown in PI. XI. II. 

 Of these, what seems to be the dominant or major system trends nearly northwest 

 and dips southwest at an angle of 80 . while the minor system traverses the rocks at 

 nearly right angles to the major, trending northeast, with dip 80 SE. Roth 

 systems seem to roughly eorrespond in trend with the similar structures in the 

 Paleozoic rocks in the mountains to the south. 



Age. — It has been determined, on paleontologic evidence, that the Anaktuvuk 

 series is Lower Cretaceous. It contains typical Aiicdla beds of Alaska. The first 

 fossils collected by the writer were found 8 miles north of the foot of the mountains. 

 Subsequently others were found at several points farther north, principally at the 

 first cross ridge on the Anaktuvuk, and in the bluff at the mouth of Willow Creek. 

 Of these fossils the most characteristic, as determined by Doctor Stanton, are 

 "AuceZla erassicollis Keyserling, or closely related forms, and are of Lower Creta- 

 ceous age. 



It should be borne in mind, however, that while its Jurassic forms prevent the 

 Corwin series from being included with the Anaktuvuk series as Lower Cretaceous, 

 it is not improbable that the discovery of such forms in the future may place the 

 lower portion of the Anaktuvuk series, now assigned to the Lower Cretaceous, in 

 the Jura-Cretaceous, since no fossils have yet been found in the extreme basal por- 

 tion of the Anaktuvuk rocks. 



Correlation. — On paleontologic grounds the Anaktuvuk series may be directly 

 correlated with the Kovukuk series, next to be described. The rocks of the former, 

 however, are free from all trace of igneous intrusions, while the Koyukuk series is 

 associated with igneous rocks," as dikes, and probabh r also as flows. 5 



Lithologically the Anaktuvuk rocks bear little or no resemblance to the Mission 

 Creek series, assigned to the Cretaceous by Spurr, c nor to the Kennicott formation 

 or the Orca series of the Copper River district. As shown in the table of provisional 

 correlation, several other series of rocks found elsewhere in Alaska have also been 

 referred to the Cretaceous — the Matanuska series by Mendenhall, between Resurrec- 

 tion Bay and Tanaua River; the Tordrillo, Holiknuk, Kolmakof, and Oklune by 

 Spurr, in southwestern Alaska; and the Cantwell conglomerate by Eldridge, d in the 

 Susbitna River region. 



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

 Geol. Survey, pt. 2, 1900, p. 477. 

 bP. 78, this paper. 



"Spurr, J. E., Geology of the Yukon gold district, Alaska: Eighteenth Ann. Rept. U. S. Geol. Survey, pt. 3, 1898. 

 rfEldridge, G. H., A reconnaissance in the Sushitna Basin, Alaska: Twentieth Ann. Rept. U. S. Geol. Survey, pt. 7, 1898. 



