LARSEN AND HUNTER: MELILITE 473 



and the resistance of the connection between them are very low, 

 it is more or less impracticable to change over to a simple bridge 

 during the adjustments. In such cases these procedures have 

 been found more . satisfactory . 



MINERALOGY. — Melilite and other minerals from Gunnison 

 County, Colorado. Esper S. Larsen and J. Fred Hunter,^ 

 Geological Survey. 



INTRODUCTION 



The minerals described in this paper were collected by the 

 authors during the summers of 1912-13 in the course of the 

 geologic mapping of the Uncompahgre quadrangle, Colorado, 

 under the direction of Whitman Cross. All but the anatase 

 are from a small complex of peculiar igneous rocks near Iron 

 Hill on the east bank of Cebolla Creek opposite the Cebolla Hot 

 Springs, and a few miles southeast of Powderhorn post office, 

 Gunnison County, Colorado. ^ 



The rocks mapped in this area are, in the order of their age, 

 a coarse-grained rock made up largely of melilite for which the 

 name Uncompahgrite is proposed, a pyroxenite which locally 

 carries segregated bodies of titaniferous iron ore, a rock related 

 to ijolite, soda syenite, cancrinite syenite, and nepheline gabbro 

 (or essexite). 



The anatase was found in veinlets along joint planes in a 

 dioritic dike which cuts the pre-Cambrian rocks in the gully 

 about half a mile northeast of the Lot Mine, a few miles east 

 of north of the mouth of Powderhorn Creek and Powderhorn 

 post office, and only a few miles north of the Iron Hill area. 



melilite 



Occurrence and association. Several bodies of rock made up 

 chiefly of melilite and for which the name Uncompahgrite is 



^ Published with the permission of the Director of the United States Geological 

 Survey. 



- All locations are given with reference to the United States Geological Survey 

 topographic map of the Uncompahgre quadrangle. 



