no. 1833. ORWIN OF MOLD AYITES— MERRILL. 485 



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 con- 

 stituent 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 lithophysse of obsidians. The 

 specimen, which is about 12 cm. by 9 cm. by 4 cm. in thickness, was 

 brought in many years ago by Prof. I. C. Russell and is labeled simply 

 "Obsidian pebble," and from the locality above given. 



These same markings I find roughly simulated on some large 

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

 Guajolote hill and Cuyamaloya, Hidalgo, Mexico. 



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

 the most strikingly billiton-like markings found on any of the ter_ 

 restrial rocks which have come under the author's observation are 

 those on some obsidians brought by Dr. F. E. Wright from a flow at 

 Hrafntinnuhyggur, near Myvatu as above noted. The specimens 

 were collected by Doctor Wright in 1909, and briefly described by 

 him at the December, 1910, meeting of the Geological Societ}^ of 

 America, an abstract of three lines only appearing in the bulletin for 

 that year. The material 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., as shown in pi. 62, fig. 6. 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 produced by the scoring of one 

 mass against another while in a plastic condition. On one surface 

 of this specimen, which unquestionably represents a more recent 

 fracture than that of the surface shown in the figure, are found only 

 the minute circular pittings such as were described as occurring on 

 the flattened areas of the specimens from Colombia. 



To still further test the possibilities of a terrestrial origin, 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 

 fluorhydric acid. The resultant forms are shown in figs. 7-9 on 

 pi. 62, fig. 9, it will be noted, compares very closely with the slag- 

 like pieces in fig. 6 of pi. 61. 



In referring to the above described materials attention needs first 

 to be called to the fact that the markings on these pebbles and 

 obsidians of known terrestrial origin more closely agree with those 

 on the tektites than do the tektitesfrom various localities agree among 

 themselves; and, further, that the etchings produced by action of 

 fluorhydric acid are practically indistinguishable from the markings 

 on some of the moldavites. Further than this, the markings on the 



