452 WASHINGTON AND LARSENI MAGNETITE BASALT 



This places it in the dofemane class and in the domitic order 

 (adirondackore), but transitional to the permitic order, hyper- 

 sthene and olivine being very low. It is in the permii-ic rang and 

 perhemic subrang — a position which is briefly expressed by the 

 symbol IV.4(5).1.1. The rang and subrang are as yet unrep- 

 resented and unnamed. The North Park District was occupied 

 by the Ute and Arapaho Indians, according to information fur- 

 nished by Mr. W. Marr of Hebron, Colorado. As the use of the 

 name Ute would suggest a locality in Utah, it seems to be prefer- 

 able to name the rang arapahase and the subrang arapahose. 



The mode of the rock can be approximately estimated from 

 the norm, the corundum, hypersthene, olivine and a little anor- 

 thite being assumed to enter the pyroxene. The mode would 

 then be about as follows: 



Bytownite 25 



Augite 15 



Iron ores 56 



Apatite 4 



The mode is, therefore, practically normative. As remarked 

 by Iddings^ this is ''at present the only known example of ex- 

 truded lava corresponding to the segregated iron ores." It may 

 be pointed out that nearly all such other iron ore rocks are asso- 

 ciated with gabbros, those of Kiruna (which are of hematite) 

 being derived from syenites, according to Geijer, and those of 

 Brazil (of which there are no analyses available) being associated 

 with highly sodic, nephehte-rich rocks. The relations of the 

 Colorado rock are too little known as yet for any discussion of 

 its associations. 



While the rock would logically be called a magnetite basalt, 

 on account of its extrusive character and mode, yet it is so 

 unique as to occurrence and chemical composition, that a spe- 

 cial name seems to be justified. For this that of arapahite is 

 suggested. 



J. P. Iddings, Igneous Hocks, 2: 332. 1913. 



