A. Hague — Leticite Rock in Wyoming Territory. 43 



Art. IV. — Notes on the occurrence of a Leucite Rock in 

 the Absaroka Range, Wyoming Territory; by Arnold 

 Hague. 



Beyond the confines of Europe occurrences of leucite as a 

 constituent of rock masses are exceedingly rare and up to fif- 

 teen years ago they were unknown. With the introduction of 

 the searching methods employed in modern petrographical 

 investigation many microscopic minerals have been detected in 

 crystalline rocks, whose presence had not previously been sus- 

 pected. In most instances, as soon as the observations were 

 published, other investigators have been able to confirm the 

 results of their fellow workers and these exceptional minerals 

 were soon reported in allied rocks in widely separated parts of 

 the world. With leucite, however, the case is somewhat differ- 

 ent, and although it is a mineral which has excited much 

 interest and considerable discussion among chemists, mineral- 

 ogists and geologists over its composition, crystallographic form 

 and mode of occurrence, the microscope, in spite of diligent 

 search, has added but one or two new localities of European 

 basalts carrying leucite and still fewer from other parts of the 

 world. 



In 1874 Vogelsang detected small crystals of leucite in the 

 basaltic rock from Gunong Bantal Soesoem, a small island of the 

 Bawean group not far from the Island of Java. In the following 

 year Prof. Zirkel* discovered an exceedingly large amount of 

 leucite in a remarkable rock from Wyoming Territory in the 

 collections of the Geological Survey of the Fortieth Parallel. 

 The mode of occurrence of this rock accompanied by a chemical 

 analysis, was published by Mr. S. F. Emmonsf in his geological 

 description of the region, he designating the group of hills 

 where the mineral occurs as the " Leucite Hills." Not until ten 

 years later was leucite again found in a new locality, when Yon 

 Chrustschoff^: determined the mineral in a rock from Cerro de 

 las Yirginas, in Lower California, and in this case he only 

 received a single hand-specimen upon which to carry out his 

 investigation. In a paper presented to the Royal Geological 

 Society of London, by Orville A. Derby, a short description 

 is given of an occurrence of leucite in a black basalt found 

 near Pinhalzinho, Brazil. § This announcement was followed 

 soon after by the discovery by Prof. John W. Judd of an 

 occurrence of leucite in Australia in a rock which, according 



* U. S. Geol. Expl. of 40th. Par., vol. iv, p. 259. 

 f IT. S. Geol. Expl. of 40th Par., vol. ii, p. 236. 

 \ Tschermak's Mittheilungen, vol. vi, 1885. 

 § Quart. Journ. Geol. Soc, vol. xliii, Pt. 3, p. 463. 



