PETROLOGICAL ABSTRACTS AND REVIEWS 581 



MgO 3.50, CaO 7.26, NezO 4.00, K2O 1.66, H2O 2.08, TiOz 0.69, 

 P2O5 0.38, CO2 2.08=99.45. The rock is considerably altered and its 

 computation is difficult. According to Osann's system it shows: 5 = 58.3, 

 a =3. 5, c = i .g, / = i4.6, n = 'j .g, ^=0.90. It is related to the Kongadia- 

 base of Hartenrod near Herboni, the diabase from Rocky Hill, New Jersey, 

 the Hunnediabase from Campo Santo, the Hunnediabase from Halleberg, 

 and the diabase from Richmond, Cape Colony. 



(The rock is an alkali diabase or an orthoclase-albite diabase). 



Albert Johannsen 



Uhlemann, Alfred. ''Die Pikrite des sachsischen Vogtlandes," 

 Tscher. Min. Petr. Mil., XXVIII (1909), 415-72. Maps i, figs, 

 17, photomicrographs 8. 



The picrites here described occur in surface flows, dikes, and intrusive 

 sheets, and are generally associated with granular diabases. The period 

 of eruption began at the end of the Silurian and ended before the beginning 

 of Middle Devonian. 



The author particularly examined the relations between the picrites 

 and the diabases, for, according to Rosenbusch, picrites are feldspar-free 

 olivine diabases, and picrite porphyrites are feldspar-free melaphyres, and 

 there are gradations from one to the other. The present study does not 

 confirm this. An analysis was made of the normal diabase, another of the 

 same rock near the contact, and a third of the picrite near the contact, and 

 while there is an enrichment of magnesia in the contact diabase, this is 

 explained by the assimilation of fragments of the picrite through which 

 the diabase was erupted. The author believes that the cause of the as- 

 sociation of diabase and picrite is not to be found in differentiation after 

 eruption, but in intratelluric differentiation from a single magma. 



In habit the picrites are coarse granular (^2 cm.), more rarely medium- 

 grained (2-4 mm.), pyroxene-olivine rocks, with less amounts of iron ores 

 and apatite, and rarely basic plagioclase. Locally there is found primary 

 biotite, rhombic pyroxene, or a globulitic and trichitic intersertal basis. 



Two analyses of the picrites were made by the author and an older' 

 one from Giimbel is given for comparison. All of them are computed in 

 Osann's system and the following formulae are found: 



^44-8, a©, Cj, '15) 



O37 , &o, Cl, IlQ, 



O42.1, 3,0, C], I19, 



which shows a remarkable resemblance between the three specimens from 

 widely separated areas. 



