AN ANALCITE-BEARING CAMPTONITE FROM NEW 



MEXICO. 



During the summer of 1899 the writer was a member of the 

 field class of Professor R. D. Salisbury, of the University of Chi- 

 cago. The party visited the Grand Canyon of the Colorado, 

 stopping on the way at several localities of interest. The first 

 halt was made at Las Vegas, New Mexico, where Miss Inez 

 Rice, a member of the class, guided the party to the butte which 

 forms the subject of this paper. I take pleasure in acknowledg- 

 ing my indebtedness to Professor Salisbury for assistance in the 

 field, and to Miss Rice for suggestions on the general geology 

 of the region. The petrographic work was done in the laboratory 

 of Columbia University, and thanks are due to Professor Kemp for 

 much kindly advice and assistance. Special thanks are also due 

 to Dr. F. Bascom and to Dr. H. S. Washington, for reading this 

 paper and for suggestions concerning it. The analysis was very 

 kindly contributed by Mr. George A. Goodell, of the College of 

 Physcians and Surgeons ; the photograph which forms the 

 accompanying illustration (Fig. 1) was obtained through the 

 courtesy of Mr. K. M. Chapman, of Las Vegas. Special thanks 

 are due to both these gentlemen. 



The Las Vegas region exhibits the general geology and 

 physiography typical of the eastern border of the Rocky Mount- 

 ains. In it are represented the two great geographical provinces, 

 the Great Plains and the Cordilleran region. These two geo- 

 graphical districts are in close correspondence with the geo- 

 logical structure. 



The Cordilleran section consists of a doubtfully Archean 

 floor, upon the base-leveled surface of which Carboniferous lime- 

 stones were deposited. This represents an overlap beyond the 

 Cambrian which underlies the Carboniferous farther north. 

 Unconformably above the Carboniferous, and situated along 



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