SOME IGNEOUS ROCKS FROM THE ORTIZ MOUN- 

 TAINS, NEW MEXICO 



I. H. OGILVIE 

 With Chemical Analyses by M. W. Adams 



The Ortiz Mountains are a deeply sculptured laccolith, lying 

 on the San Pedro quadrangle, some twenty-five miles east of Albu- 

 querque. They are roughly circular in outline with a diameter of 

 about five miles, and have a relief of about 3,000 ft., the highest 

 peak rising to an altitude of 8,998 ft. They afford interesting data 

 on erosion in an arid climate; on Mesozoic stratigraphy and paleon- 

 tology; on the events of the Pleistocene period in the region south 

 of the ice sheets ; and on petrology. The present paper is preliminary, 

 and deals with a few of the more conspicuous rock types. 



The quantitative system is used in classification, the names being 

 based on analyses. The following table indicates the rock types 

 represented. 



TABLE I 



The distribution of these types is found to be noteworthy: The 

 main mass of the laccolith is of the more femic types, essexose and 

 Auvergnose (andesites) ; the sheets which border the mass are of the 

 most salic types, the persalanes (dacites) ; while the spurs and flanks 

 of the mountains, lying between the above are of the intermediate 

 types. It should however be noted that all of the rocks are inter- 

 mediate when compared with igneous rocks in general. 



230 



