DEC. 4, 1921 WASHINGTON : OBSIDIAN FROM COPAN 481 



Borax cr^^stals remain in the mud of Borax Lake although the water 

 is not now saturated with borax. It is not unusual to find certain 

 crystallized salts in the bottom mud of a lake containing water that 

 is not saturated with those salts. Water from the bottom mud and 

 lower is also frequently more concentrated than the lake water. Such 

 relations have been noted in the Wyoming lakes carrying sodium 

 sulfate, in the Nebraska lakes carrying potassium salts, and in the 

 Great Salt Lake, where Glauber's salt has been found below sand 

 and clay. The explanation probably is that in the coldest or driest 

 weather crystals are deposited and fall to the bottom where they be- 

 come covered with silt and clay. The reverse process of solution, 

 being chiefly dependent on diffusion, is too slow to occur in the alter- 

 nate warm or wet seasons or even in several such seasons. Certain 

 salt deposits may therefore owe their origin in some cases to extreme 

 or unusual conditions rather than to average conditions, provided 

 they become silted over. 



PETROLOGY. — Obsidian from Copan and Chicken Itza} Henry 

 S. Washington, Geophysical Laboratory, Carnegie Institution of 

 Washington. 



OBSIDIAN FROM COPAN 



In 1920, during his study of the Maya ruins at Copan, Honduras, 

 Dr. Sylvanus G. Morley obtained a number of obsidian cores, that is, 

 the remnants of rock nodules from which knives and other implements 

 had been flaked off by the ancient Maya. Dr. Morley very kindly gave 

 these cores to me for examination, a courtesy for which I would express 

 mv thanks. It appears that many such cores are found by the natives 

 among the ruins and along the valley floor, and that nodules of ob- 

 sidian are said to occur in the tuffs of the neighborhood. As such cores, 

 valueless in Copan, would scarcely be articles of trade, it may be safely 

 assumed that the obsidian of those studied comes from the vicinity 

 of Copan. 



Little is known of the volcanic rocks of Central America. Obsidian, 

 dacite, andesite, and basalt are mentioned and described briefly by the 

 few petrologists who have dealt with the subject, but (except for the 

 rocks of Panama and the Canal Zone) there are only five analyses of 

 Central Am.erican rocks, and only one of these is of an obsidian. 



The cores are from 10 to 13 cm. long, and from 2.5 to 3 cm. at the 

 greatest thickness. They are roughly spindle-shaped (Fig. 1), with 

 the greatest width near the middle in some of them, but near one end in 



1 Received November 4, 1921. 



