W. Cross — Igneous Rocks in Wyoming. 129 



that is the tone of the mass where they are developed. Nearly 

 one- third of the rock is amorphous, but the multitude of minute 

 crystals embedded in it, the cloudy zone about the perofskites, 

 and the globulitic particles mentioned, make this base trans- 

 parent only in the thinnest sections. As will be shown later 

 on, this glassy base contains silica, alumina, and the alkalies, in 

 nearly the ratio found in leucite. 



For this rock, consisting of diopside and phlogopite in pre- 

 dominant degree, and with leucite or a glassy base correspond- 

 ing to it, I propose the name madupite, from the Shoshone 

 Indian madupa, meaning sweetwater,* the name of the County 

 in which the locality is situated. A definition, with discussion 

 of the relationships of madupite, will be found in a later sec- 

 tion of this article. 



Chemical Composition of the Rocks Described. 



In the table below are given several analyses of wyomingite, 

 orendite and madupite, of the phlogopite and diopside isolated 

 from these rocks, and of a few related rocks for purposes of 

 comparison. Under I is an analysis by Pawel, made for Zirkelf 

 and published in his German resume of the 40th Parallel 

 report; II is by R. W. Woodward, and was published by 

 Emmons^ (I and II were presumably made on the same 

 material) ; III is of wyomingite from the Boar's Tusk ; IV of 

 wyomingite from the 15-mile spring ; V is of orendite from 

 the 15-mile spring; VI of orendite from North Table Butte; 

 YII of madupite from Pilot Butte ; VIII of phlogopite from 

 wyomingite of Boar's Tusk ; IX of diopside from wyomingite 

 and madupite. The analyses III to IX, inclusive, are all by 

 W. F. Hillebrand, whose many painstaking and reliable 

 analyses of igneous rocks form a most important contribution 

 to petrography. Analysis X, by H. N. Stokes, is of " leucitite " 

 from the Bearpaw Mountains, Montana, described by Weed 

 and Pirsson (tiiis Journal (4), vol. ii, 1896, p. 147). No. XL 

 by E. B. Hurlburt, is of missourite, also from the Highwood 

 Mountains and described by Weed and Pirsson (this Journal 

 (4), vol. ii, 1896, p. 321). 



* According to information kindly given me by Mr. W. J. McGee, of the 

 Bureau of Ethnology. 



f Ueber die Krystallinischen Gesteine langs des 40 ten Breitegrades in Nord- 

 west-Amerika. Benchte der k. sachs. Gesellschaft der Wissenschaften, Jan., 

 187.7, p. 239. 



\ Reports of the Fortieth Parallel Survey, vol. ii, Descriptive Geology, 1877, 

 p. 237. 



