04 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



Judging' from exposures observed in the region of the Anaktuvuk. the thickness 



of this limestone formation is probably a little over 3,000 feet. 



Struct are. — The entire area of the Lisburne formation here considered is deeplv 

 involved in the system of faulting and disturbed blocks referred to under the head- 

 ing "Stirrer series." As viewed from the Anaktuvuk Valley, looking either easi 

 or west (see section on PI. Ill; also tig. 4 and PL X, Z>), the Lisburne series reveals 

 but little of the disturbance it has undergone. On the southwest, however, toward 

 Contact Creek, the rocks have been folded and broken into blocks, which in some 

 instances are highly tilted. The fault on the west side of the Anaktuvuk, shown on 

 the right of fig. 4, probably represents the westward extension of the same fault 

 that gave rise to the scarp along the northern edge of the Stuver series, which series 

 however, has not here been brought to view. At the north base of the mountains, 

 west of the Anaktuvuk, the Lisburne formation disappears beneath the covering of 

 glacial drift with a dip of 60° to the north. East of the Anaktuvuk it similarly dis- 

 appears beneath the drift, but with an opposing dip at an angle of 75° S., against 

 the fault scarp of the Stuver series, as shown in the section on PI. III. Between 

 these two localities the Stuver series probably attains a steep westerly dip, of which 

 there is some suggestion along the north edge of the vallej 7 , or a portion of the val- 

 ley may be traversed by a north-south fault extending from the north edge of the 

 mountains to the southern limits of the Stuver series. 



In certain localities, notably on the south side of the Anaktuvuk, the Lisburne 

 is cut by a close jointing, trending N. 27° E., with dip southeast-east at an angle 

 of 85°, dividing the rocks into thin slices from 2 to 8 inches in thickness. 



There can be but little doubt that the faulting between the Lisburne and the 

 Fickett series continues eastward and connects with that along the southern edge 

 of the Bettles series, on Koyukuk and Chandlar rivers. Its alignment with the 

 boundary of the Bettles series, as located in a previous year's work," is shown on the 

 geologic map, PL III. 



Age. — The most convenient disposition to make of the Lisburne formation would 

 be to include it with the Fickett series and call the group Carboniferous and Devonian, 

 since both Carboniferous and Devonian fossils occur freely in the stream gravels of 

 the upper John and Anaktuvuk rivers, and none of the fossils found in place were 

 sufficiently well preserved for identification. On lithologic grounds, however, the 

 Lisburne formation can be set apart as qu ; te distinct from the Fickett series, which 

 it also seems to underlie. Therefore, on the basis of the Devonian fossils found in 

 detached fragments of rock on the surface of the formation near the top of the 

 mountains, and on the lithologic similarity of the rock attached to these fossils to that 

 of the Lisburne formation, the formation is provisionally referred to the Devonian. 



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

 Geol. Survey, pt. 2, 1900, pi. lx. 



