COLVILLE SERIES 249 



it constitutes the lower three-fourths, or 150 feet, of the section exposed, 

 and includes all the above noted rocks, excepting the unconsolidated 

 silts. These latter are free from lignitic remains, and on the basis of 

 their invertebrate fossils are assigned to the Pliocene. Accordingly the 

 Pliocene, so far as observed, consists of nearly horizontal stratified beds 

 of mostly fine gray slate and ash -colored calcareous silts, containing 

 faunal remains. By conservative estimate the thickness of the Colville 

 series is probably 500 or 600 feet, and, judging from topography, it prob- 

 abty has a very great extent in an east and west direction, possibly reach- 

 ing the coast in the region south of point Barrow. 



Though the series, as shown in plate 43, has been slightly faulted, 

 folded, and crowded from the inland direction, it is on the whole but 

 little disturbed. The beds lie nearly horizontal or dip gently north or 

 northwestward at a low angle of 4 or 5 degrees, as shown in plate 43. 

 The lower part of the series is supposed to be Oligocene on the ground 

 of the presence of the lignite beds and vegetable remains it contains and 

 its resemblance to known similar beds occurring elsewhere in Alaska, 

 and also on the ground of its relation to the Pliocene silts which it im- 

 mediately underlies. Lignitic shale examined b}' Doctor Dall is sup- 

 posed to contain the form of Sequoia langsdorffi Heer. The upper part 

 of the series is assigned to the Pliocene on the basis of its fossil forms, 

 which have been reported by Doctor Dall as follows : 



Chrysodomus, 2 species. Macoma incongrua von Martens. 



Amauropsis. Astarle semisulcata Leach (possibly 



Tachyrhynchus polaris Beck. Quaternary intrusion). 



Macoma frigida Hanley. Saxicava arctica L. 



Pleistocene 



the deposits 



Besides the present stream gravels, the most important Pleistocene 

 deposits traversed by the section, but not represented on it by reason of 

 the small scale, are the Goobic sands, glacial deposits, ground ice, and 

 muck. 



GOOBIC SANDS 



This formation is a surficial deposit of brownish sand or loam about 

 10 or 15 feet in thickness, which, like a continuous mantle, overlies the 

 beds of the Colville series unconformably, as shown in plate 43 at the top 

 of the bluff just above the light-colored triangular exposures of Pliocene. 

 It seems to be distinct from the Colville series and to be persistent over 



XXXVII— Boi,r,. Geol. Soc. Am., Vol 13, 1901 



