2o8 WILLIAM H. EMMONS 



Parkj described by Mr. Iddings.^ It also resembles that of a 

 homblende-mica-porphyry from Cliff Creek, West Elk Mountains, 

 Colorado, described by Dr. Whitman Cross, ^ and a mica-diorite 

 from Lippenhof, N. Tryberg, Schwartzwald, Baden, described by 

 Dr. G. H. Williams.3 



I. Norm II. Mode 



Quartz 19 • 5° Quartz 22.9 



Orthoclase 20.57 Orthoclase 17.8 



Albite 32 . 49 Albite 30 . 7 



Anorthite 12.51 Anorthite 10.3 



Hypersthene 4 . 80 Hornblende 9.7 



Diopside 3 . 02 Biotite 4.2 



Magnetite 3 .02 Magnetite and Ilmenite 4.1 



Ilmenite 1.22 Apatite 0.3 



Hematite o . 80 -r ^ 1 



iotal 100. o 



Apatite o ■ 34 



98.27 



Water 1.41 



Total 99 . 68 



VARIETY B. HARTZOSE: GRANODIORITE-PORPHYRY 



At the eastern edge of the stock about 30 rods north of the wagon 

 road from Cowles to the Yellowstone Park a small tongue extends from 

 the stock into gneiss. The specimen, taken 28 yards south of the 

 northern edge of this tongue, is dark gray, fine-grained, and contains 

 numerous phenocrysts of yellow feldspar, together with a smaller 

 number of phenocrysts which appear from their form to be horn- 

 blende, but which in some cases have the luster and cleavage of mica. 



Under the microscope the groundmass of the rock is seen to be 

 composed of small interlocking anhedra of poikilitic quartz and 

 alkali feldspar, a large number of minute pyroxene prisms, and a 

 few anhedra of magnetite, plagioclase (oligoclase-andesine), and 

 biotite. The porphyritic bodies, which in hand specimens appear 

 to be crystals of single minerals, are found to consist of several minerals. 

 These aggregations are of two kinds: those composed mainly of 

 feldspar, and those composed mainly of ferromagnesian minerals. 



1 Mon. XXXII, U. S. Geological Survey, p. 261, 1889. 



2 Fourteenth Annual Report, U. S. Geological Survey, Part II, p. 227, 1894. 



3 Neues Jahr., Band II, p. 624, 1883. 



