450 REPORT OF NATIONAL MUSEUM, 1899. 



stratified with the shales, the lowermost bed of 9 feet thickness being 

 underlaid by fire clay. The origin of the material is in doubt, the 

 earlier writers regarding it as a bituminous coal coked by the heat of 

 intrusive rocks. Later writers throw doubt upon this by stating that 

 there are in the vicinity no intrusives of such size as to warrant any 

 such assumption. 



[Tses. — The material is said to l)urn without smoke or soot, like 

 anthracite, and to have been used for domestic purposes. 



UiNTAiTE ; GiLSONiTE. This is a black, brilliant, and lustrous vari- 

 ety of bitumen, giving a dark-brown streak, breaking with a beautiful 

 conchoidal fracture, and having a hardness of 2 to 2.5 and a specific 

 gravity of 1.065 to 1.07. It fuses readily in the flame of a candle, is 

 plastic, but not sticky while warm, and unless highl}^ heated v>'ill not 

 adhere to cold paper. Its deportment is stated to be much like that 

 of sealing wax or shellac. Like albertite and grahamite it dissolves 

 in turpentine and is not soluble in alcohol. It is a good nonconductor 

 of electricity, but like albertite becomes electric by friction. Its com- 

 position as given is: Carbon, 80.88 per cent; hj^drogen, 9.76 per cent; 

 nitrogen, 3.30 per cent; oxygen, 6.05 per cent, and ash, 0.01 per cent. 

 Specimens Nos. 62379, 53355, U.S.N. M., are characteristic. 



Occurrence. — According to George H. Eldridge^ the gilsonite de- 

 posits of Utah occur filling a series of essentially vertical fissures in 

 Tertiary sandstones lying within the Uncompahgre Indian Reserva- 

 tion, or in its immediate vici.nity. The fissures have smooth, regular 

 walls and vary in width the sixteenth of an inch to 18 feet, and in 

 length from a few hundred yards to 8 or 10 miles. 



The larger veins are somewhat scattered, one lying about ?>\ miles 

 east of Fort Duchesne, a second in the region of the Upper Evacua- 

 tion Creek, and the three others of most importance in the vicinity 

 of the White River and the Colorado-Utah line. Besides these there 

 is a l-l-inch vein crossing the western boundar}^ of the reservation 

 near the fortieth parallel; another about equal size about 6 miles south- 

 east of the junction of the Green and White rivers; a third in the 

 gulch 4 or 5 miles north of Ouray Agency, west of the Duchesne River, 

 and a number from one-sixteenth of an inch to a foot in thickness in 

 an area about 10 miles wide, extending from Willow Creek eastward for 

 25 miles along both sides of the Green and White rivers. The veins 

 are sometimes slightly faulted, and often pinch out to mere feather 

 edges. The filling nraterial is quite structureless excepting where, as 

 near the surface, it has been exposed to the atmospheric influences, 

 where it shows a fine pencillate or columnar structure at right angles 

 to the walls. The walls of the veins themselves are impregnated with 

 the gilsonite for a distance of several inches, but all indications point 



^Seventeenth Annual Report U. S. Geological Survey, 1895-96, Pt. I, p. 915. 



