Chuitna River field is part of the Beluga-Yentna field in the upper Cook Inlet basin. Coal occurs in the Tertiary rocks of entirely continental origin. In order to characterize the vertical variation of coal more completely and to understand the environments of coal deposition, a drill hole was cored to a depth of 290 ft with the help of Diamond Alaska Coal Co. The core included five coal beds: Blue (bottom 15 ft), Red 3 (13 ft), Red 2 (26 ft), Red 1 (16 ft), and Purple (5 ft). These beds were sampled foot by foot and were characterized for ash, moisture, ash fusibility, ash composition for major oxides and trace elements, vitrinite reflectance, and petrographic composition under normal incident light as well as fluorescent illumination. A palynological evaluation is in p ogress. Ultimate analyses were made for 5-ft intervals.

Ash composition of foot-by-foot samples varied widely. For example SiO₂ ranged from 0.58 to 65%, Fe₂O₃ from 1.97 to 57%, CaO from 2.5 to 35%, P₂O₅ from 0.07 to 17%, and Ba from 0.19 to 3.7%. Petrologic analyses showed less drastic variations within a seam. The wide variation in ash composition, particularly of iron and silica, among others, is indicative of periodic changes in pH of the swamp environment. Lack of high inertinite zones within the seams studied shows that the swamp was not subjected to drastic changes in the water table and that the subsidence kept pace with peat accumulation during the formation of each of the seams.

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