PETROLOGICAL ABSTRACTS AND REVIEWS 713 



Tyrrell, G. W. "The Igneous Geology of the Cumbrae Islands, 



Firth of Clyde," Trans. Geol. Soc. Glasgow, XVI (1916-17), 



244-74, figs. 5. 



Most of the igneous rocks of the Cumbraes are of Lower Carboniferous age. 



They are predominatly basahic and originally covered from 2,000 to 3,000 



square miles. 



Tyrrell, G. W. "The Picrite-Teschenite Sill of Lugar," Quart. 

 Jour. Geol. Soc, LXXII (1917), 84-131, pis. 2. 

 The Lugar sill in the west of Scotland is foimd to be made up of a complex 

 of rocks belonging to the analcite series. It forms a mass 140 feet thick and 

 was intruded into cold rocks, as shown by chilled contacts at top and bottom, 

 giving a fine-grained teschenite for a thickness of 10 feet. Beyond the mar- 

 gins, both top and bottom, the rock passes into coarse teschenite. In the 

 interior the sill is divided into at least three bands by some process of differen- 

 tiation or by successive intrusions, giving first a band of ultra basic rock— 

 picrite and peridotite of coarse texture — occupying the major part of the whole 

 mass. The picrite forms the upper part of the ultrabasic stratum, the perido- 

 tite the lower. Above the picrite is a band about 10 to 15 feet thick of fine- 

 grained, basic, nephelite rock of the theralite family. Overlying the picrite, 

 in places, is a peculiar rock to which the name lugarite has previously been 

 given. It appears to be intrusive in the picrite, for veins of similar material 

 traverse the latter rock in various places. Three of the teschenites are 2319' 

 of the reviewer's system, and two are 3320, the difference being the absence 

 of orthoclase and the predominance of the dark constituents in the latter. Two 

 chemical analyses are given as well as five more calculated from Rosiwal 

 measurements. Two lugarites are 2320. (A rock described as lugarite in 

 Geol. Mag., 191 5, 363, is here called a lugarite-like rock. It is 2218'.) One 

 chemical analysis and two calctdated analyses from Rosiwal measurements are 

 given. As for the cause of the differentiation, the author thinks that the hy- 

 pothesis of sinking of heavy crystals is weU attested in the Lugar magma as a 

 whole, but that the differentiation took place prior to its eriaplacement. The 

 material was injected in successive intrusions, the teschenite first in cold rocks 

 and formed the fine teschenite borders. While stiU cooling, but probably 

 aheady solid, the picrite was intruded along its center plane. Here differentia- 

 tion took place mainly by the sinking of olivine-crystals. Later, while probably 

 still partly liquid, it was intruded by a smaU mass of lugarite. 



Velde, Luise. "Die silikatischen Einschliisse im Basalte des 

 Biihls bei Kassel," Abhandl. d. Senckenberg. Naturf. GeselL, 

 XXXVII (1920), iii-35> pis. 4- 

 The silicic inclusions in the Biihl basalt in many cases preserve the charac- 

 teristics of the original rocks from which they were derived, namely, sandstones 



