REVIEWS 665 



The concluding chapter of Mr. Weed's report contains notes on 

 the ore deposits, under the heading : " The Ores, Veins, and Mines." 

 The ores are chiefly those of silver, silver-lead, and gold. Sapphire 

 mines occur in Fergus county, and are said to be the most valuable 

 gem mines in the country. Deposits of limonite and hematite are 

 found in a number of localities and will some day be developed eco- 

 nomically. 



The petrography of the igneous rocks by Professor Pirsson is a 

 rather full account of the rocks, their mode of occurrence and field 

 relations, texture, and microscopical characters, together with their 

 chemical composition and the estimated quantitative mineral composi- 

 tion. It also considers the general petrology of the region, and closes 

 with a discussion of magmas by graphic methods, and the absorption 

 of sediments by magmas. 



The rocks are subdivided into (a) granular non-porphyritic rocks, 

 [b] acid feldspathic porphyries, (c) lamprophyres, (d) effusive rocks. 

 In the first group are found representatives of syenites, monzonites, 

 diorites, shonkinites, and aplites. Among the syenites is analcite- 

 (nephelite) svenite, which, unfortunately, has not been analyzed 

 chemically. Syenite, monzonite, and shonkinite occur together as 

 differentiation products of one rock body at Yogo Peak. In the 

 shonkinite the proportion between the dark and the light constituents 

 is ff — that is, the former preponderate. The second group contain 

 representatives of granite, syenite, and diorite classes, and constitute 

 the laccoliths and many of the intruded sheets. Among these rocks 

 there are many transitional types, the transitions being, in several cases, 

 of much more importance locally than the more commonly-known 

 types. Further, these transitions occur not only in different masses, 

 but often in the same mass. The third group includes minettes, which 

 are rather common in this district, besides nephelite-minette, vogesite, 

 and analcite-basalts. Among the minettes is a variolitic facies, the 

 small varioles being spherulites of feldspar. Nephelite-minette is a 

 new variety of rock belonging to the monchiquite-alnoite series of 

 Rosenbusch. Analcite-basalts occur as dikes in several localities. In 

 one case the rock is estimated to contain 49.5 per cent, of analcite, the 

 remainder being pyroxene, olivine, and magnetite. A rock closely 

 allied to analcitc-basalt carries the sapphires mined in this region. 

 The sapphires are considered as having resulted from the absorption 

 of fragments of clay shale included in the magma at the time of its 



