204 BULLETIN 94, UNITED STATES NATIONAL MUSEUM. 



in color, and show under the microscope the characteristic black hair- 

 like trichites. The surfaces are roughened by pits and grooves, and 

 in addition the entire surface is shagreened. 



(3) Obsidian pehhles, near Marsh, Idaho (Cat. No. 77784).— These 

 pebbles, again, are of ordinary black obsidian, and were collected by 

 Dr. W. Lindgren, of the U. S. Geological Survey, in gravel beds some 

 4| miles north and 20 degrees west of Marsh. The surfaces are 

 everyAvhere pitted and grooved, but the elongated, curvilinear, and 

 lunar crater forms so characteristic of the billitonites are quite lack- 

 ing. The surfaces are coated with a thin, mammillated crust, which 

 is in part a secondary deposit of iron. 



(4) Ohsidian j>ebhle, High Rock Canyon, Nevada (Cat. No. 

 35270). — This pebble is of coal black obsidian, only faintly trans- 

 lucent on the thin edges. The surface is etched in a manner sug- 

 gestive of the billitonites, even to the nearly circular lunar crater 

 forms, as they may be termed. The surface is also considerably 

 abraded as though the pebble had been rolled about on a beach, and 

 the bottoms of the grooves, or flutings, are coated with a dull, 

 brown-red material, which seems to be an original constituent rather 

 than an extraneous substance deposited from the water as was at 

 first supposed. It is probably a devitrification product similar to 

 that found in the lithophysae of obsidians. 



These same markings are roughly simulated on some large 

 weathered obsidian pebbles sent by Dr. J. Aguilera from between 

 Guajolote Hill and Cuyamaloya, Hidalgo, Mexico. (Cat No. 77802.) 



(5 ) Obsidian, near Myvatn, Iceland (Cat. No. 77616) . — Perhaps the 

 most strildngly billitonite-like markings found on any of the terres- 

 trial rocks are those on some obsidians brought by Dr. F. E. Wright 

 from a flow at Hrafntinnuhryggur, near Myvatn, in 1909. The ma- 

 terial is a highly lustrous jet black glass, the outer surfaces of which 

 are grooved and etched to a maximum depth of 2 or 3 mm. Not 

 only are the lunar crater forms here in evidence, but there are also 

 elongated, nearly straight grooves which, but for the position they 

 occupy on the surface, might at first be thought to have been pro- 

 duced by the scoring of one mass against another while in the plastic 

 condition. On one surface of this specimen are found only the 

 minute circular pittings such as were described as occurring on the 

 flattened areas of the specimens from Colombia. 



To test the possibilities of a terrestrial origin for these markings, 

 fragments of dark obsidian from near Reno, Nevada, and Yucca, in 

 Mohave County, Arizona, were submitted for a few days to the action 

 of dilute fiuorhydric acid. The resultant forms are shown in the 

 specimens numbered 88663. 



Attention should be called to the fact that the markings on these peb- 

 bles and obsidians of known terrestrial origin more closely agree with 



