44 A. Hague — Leucite Bock in the 



to him, had many points of resemblance to the rock of the 

 Leucite Hills. This leucite rock is found near Bourke, in the 

 colony of New South Wales, about 450 miles northwest from 

 Sydney. Last year Mr. J. S. Hyland* described a small 

 collection of rocks from Mt. Kilimanjaro in Africa, among 

 which were specimens of basanite carrying small crystals of 

 leucite along with nepheline. Within the last few years we 

 have the announcement of the detection of leucite in Asia, 

 Africa, South America and Australia, but as yet from only 

 one locality in each of these great land divisions of the globe. 

 Up to the present time the two North American occurrences 

 already mentioned, are the only instances rejDorted from this 

 country ; new localities, therefore, are not without interest. 



In the early autumn of 1888, the writer, while engaged in 

 geological explorations m the southern end of the Absaroka 

 Range in northwestern Wyoming, collected a specimen of basic 

 lava which subsequently proved to carry a considerable amount 

 of microscopic leucites. Unfortunately, only a single hand- 

 specimen was obtained, slight importance being attached to the 

 rock at the time, as it was not found in place, but taken from a 

 bowlder whose precise mode of occurrence was unknown. The 

 bowlder was found in the gorge of the Iskawooa River, the 

 main north branch of the South Fork of the Stinking Water, 

 the river rising in the summits of the mountains not far from 

 the sources of the Yellowstone. The Absaroka range pre- 

 sents one of the boldest and wildest regions of the Rocky 

 Mountains ; it stretches in a north and south line for over one 

 hundred miles, with an average width of more than twenty 

 miles, extending from about the 45th parallel, the boundary 

 between Montana and Wyoming, southward until it joins the 

 Wind River range. Geologically, the Absaroka range throughout 

 its entire length and breadth, is formed of enormous masses of 

 volcanic lavas, no other rocks being known in the more elevated 

 portions. For the most part these lavas are made up of coarse 

 and fine breccias and agglomerates of basic an desites and tran- 

 sition rocks to true basaltic breccias. Deep and profound 

 canons afford admirable sections through this volcanic material, 

 two, three and four thousand feet in thickness. It was while 

 engaged in examining these lavas and their relations to the 

 wonderful system of dikes which penetrate them, that the 

 bowlder was noticed. Along the gorge no rocks are known 

 other than the great sheets of lava and the intrusive dikes. 

 The configuration of the country precludes the possibility of 

 the leucite bowlder having been transported there from any dis- 

 tant region. 



* Tschermak's Mittheilungen, vol. ix, 1888. 



