GOOSE CREEK HILLS. - 515 



SECTION III. 



GOOSE CREEK HILLS TO TUCUBITS MOUETADi^S 



BY S. F. EMMONS. 



Goose Ceeek Hills. — This name has been given to a group of hills which 

 lie directly north of the Ombe Mountains and form the southern continua- 

 tion of a high range of mountains of the same name, extending north into 

 Idaho, beyond the limits of the map. Immediately north of the hills, as 

 represented on the map, extends a north and south ridge, having a general 

 anticlinal structure, made up largely of white, close-grained quartzites, 

 with blue and white, fine-grained, siliceous limestones. These rocks of the 

 range show evidence of considerable metamorphic action and a large devel- 

 opment of vein-material. The quartz veins have a general north and south 

 trend, often being traceable for 6 or 7 miles, with a thickness of as much 

 as 6 or 8 feet. In several localities upon the east side were found a new 

 and undescribed species belonging to the genus Fusilina, associated with 

 a poorly-preserved Produdus, proving clearly the Carboniferous age of 

 the limestone, while the quartzites have a general lithological resem- 

 blance to those of the Weber formation. 



That portion of the hills which is included within the limits of the map 

 is principally covered by rhy elite flows, beneath which are obscure outcrops 

 of limestones, which have been referred to the Upper Coal-Measure group. 

 The rhyolites present a great variety of texture and composition, and con- 

 stitute a very interesting group of rocks. In an interior valley of the hills 

 is an outcrop of granite-porphyry, showing a dome-shaped mass, only exposed 

 in the lowest points of the valley. It is a greenish-gray rock, showing large 

 crystals of pink-white orthoclase imbedded in a greenish-gray mass, made 

 up of decomposed hornblendes in a gray felsitic groundmass. Under the 

 microscope, the groundmuss is seen to be made up of hornblende, orthoclase, 

 plagioclase, and quartz. The larger feldspars are altered into an opaque 

 mass, in which, in some places, traces are seen of a former triclinic striation. 



