486 JOURNAL OF THE WASHINGTON ACADEMY OE SCIENCES VOL. 11, NO. 20 



TABLE 3 



Norms of Pantellerite Obsidian and Cognate Rocks 



(1) (2) (3) (4) 



Quartz 35.34 31.14 27.60 31.32 



Orthoclase 27.24 29.47 25.02 26.69 



Albite 24 .10 22 .01 20 .44 30 .92 



Acmite 6.47 9.24 17.56 6.93 



Sodium metasilicate... 2.68 1.10 1.34 none 



Diopside 3.10 2.57 1.21 0.65 



Hypersthene 0.23 0.46 4.10 0.50 



Magnetite none none none 1 .39 



Ilmenite 0.15 1 .22 1 .67 none 



Apatite none 0.34 0.34 none 



(1) Obsidian, Chichen Itza. (I) II. 3".1.3. 



(2) Comendite, Pantelleria. (I) II. (3) 4.1.3. 



(3) Pantellerite, Pantelleria. II. 3(4). 1.3. 



(4) Comendite, Sardinia. I (II). (3) 4.1.3. 



of these types are rather rare and are invariably connected with 

 characteristically sodic comagmatic regions. We know of no such 

 sodic region in or near Central America or in southern Mexico, the 

 nearest being the locality of nephelite syenite, in the State of Tam- 

 aulipas,^ in northeastern Mexico. The lavas here, however, are 

 apparently dacite, andesite, and basalt, Finlay mentioning no highly 

 sodic lavas, such as phonolite or pantellerite. There are occurrences 

 of pantellerite and other sodic lavas in western Texas, and I have 

 pointed out elsewhere the probable existence of a zone of sporadic 

 occurrences of sodic rocks along the eastern border of the North 

 American continent, and that it probably continues down along the 

 east coast of South America. 



As has been said above, we know very little of the volcanic rocks 

 of Central America, or of Mexico, for that matter, so it is quite possible 

 that another isolated district of sodic rocks occurs in southern Mexico 

 or northern Central America. The finding of these beads made of 

 pantellerite obsidian in the Chichen Itza cenote gives warrant for 

 this belief, which is further strengthened by the abundance of jade 

 objects found in this general region, the material of which may be 

 considered of Mexican or Central American provenance. 



It would seem to be clear, from the descriptions above, that the 

 Chichen Itza obsidian is derived from a volcanic source quite distinct 

 and, we may reasonably suppose, far distant from that of the Copan 

 cores. The occurrence of two such widely different obsidians, one 

 of which belongs to a chemically very peculiar kind of rock, serves 



* G. I. Finlay. Ann. N. Y. Acad. Sci. 14: 247. 1904. 



