PALEOZOIC ROCKS, LISBURNE FORMATION. 63 



apparently the same formation, consisting of limestone and shale, occurs. On the 

 AnaktuTuk the formation occupies a belt 15 or more miles in width, extending 

 north and south along the valley. Toward the west the belt narrows and appears to 

 soon be delimited on the southwest by the fault scarp of Contact Creek, and, farther 

 west, by the Carboniferous of the Fickett series; while to the east of the Anaktuvuk 

 it seems to widen. The westward extension of the formation may, however, some- 

 what exceed that represented on the map before it disappears beneath the Carbonif- 

 erous, for the mountains south of Contact Creek were not ascended. 



Where examined along Contact Creek, the north side of the valley for several 

 miles consists of a steep wall, or fault scarp, of the Lisburne limestone, similar to 

 that forming the scarp along the Anaktuvuk Valley on the east; while the rocks 

 directly opposite, on the south side of the valley, less than three-fourths mile distant, 

 are Carboniferous quartzite and conglomerate of the Fickett series. Northwest of 

 this locality, however (as shown in PL IV, B, a view looking westward from the 

 south edge of a Lisburne fault block near Contact Creek), the Lisburne, still forming 

 the crest of the axis, with an elevation of about 6,500 feet, is less disturbed. The 

 beds on the right, which show a marked increase in shale at the expense of the lime- 

 stone, dip northward toward the base of the range, while farther west the Lisburne 

 seems gradually to disappear beneath the Fickett series as a broad anticline, with the 

 longer limb sloping gently southward and the shorter dipping more steepty north- 

 ward, and probably playing an important part in forming the steep north front of the 

 range, as has been shown to be the case to the east of the Anaktuvuk Valley. 



In the foreground of PL IV, B, the Lisburne extends all the way across the 

 field from left to right, but the sculptured cirque topography forming the top of the 

 mountains in the left background lies in the slate and quartzite of the Fickett series, 

 which, to the northwest, seems to overlie the Lisburne and form the crest of the 

 range, and probably also descends the north slope and underlies the Mesozoics of the 

 Anaktuvuk Plateau at the north base of the mountains. 



The rocks of the Lisburne formation may be characterized for the most part as 

 medium-bedded semicrystalline limestone of impure white or gray color. They 

 weather gray, light rusty brown, or chocolate. They form the mountains that rise 

 to a height of 2,500 to 3,000 feet above the floor of the Anaktuvuk Valley. Near 

 the summit (see PL X, B, and fig. 4) occur two beds of intercalated shale, each 

 apparently several hundred feet thick, and containing some thin layers of dark-gray 

 limestone. 



On the east the extent of the formation is unknown. On the south it is appar- 

 ently in contact with the Carboniferous, while in descending the slope of the moun- 

 tains on the north it disappears heneath a mantle of glacial till, where, judging from 

 the topograph}-, it is probably soon met and overlain by Mesozoic strata, which prob- 

 ably rest unconformably upon it at this point. (See. fig. 4, p. 51.) 



