405 



cooling was divided into two stages. The first stage (arrangement No. 2) 

 was prolonged lor forty-eight hours ; the second stage (arrangement 

 No. 4) for the same time. During the first stage olivine crystals were 

 formed measuring on the average '5 mm. x '2. These were similar in 

 form and optical characters to those occurring in the natural basalts. 

 Magnetite and picotite also crystallized out in octahedra ('02 mm.) during 

 this stage. During the second stage microlites of labradorite ('15 mm. x 

 03 mm.) elongated in the direction of the edge 001 : 010, twinned 

 according to the albite plan and giving a maximum extinction of 30 

 were formed together with short microlites ('05 x '025) of augite and 

 some magnetite and picotite ( - 005). A small quantity of matter remained 

 in the amorphous condition. 



(4) Nepheline-augite rock. A mixture of three parts of nepheline 

 and 1*3 of augite gave, after cooling for two days, under the arrangement 

 No. 4, an association of nepheline and augite. The nepheline occurred in 

 short hexagonal prisms ('02 mm.), the augite in greenish yellow crystals 

 ('01 x - 004). There were also some larger microlites of augite. 



(5) Leucite-augite rock. A mixture composed of nine parts of leucite 

 and one of augite maintained for three days under the arrangement No. 2 

 gave an association of leucite (mean diameter -06), greenish pyroxene 

 (025 x '003), magnetite ('005), and glass of the same colour as 

 the augite. 



(6) Leucite-labradorite-augite rock (leucotephrite). A mixture of 

 silica, alumina, potash, soda, magnesia, lime and oxide of iron representing 

 one part of augite, four of labradorite and eight of leucite was fused and 

 then maintained for two days under the arrangement No. 2, and for 

 a corresponding period under the arrangement No. 4. The result was 

 a mass composed of leucite crystals (mean diameter '35). microlites of 

 labradorite ('05 x -02), microlites of augite ( - 025 x '005) and magnetite. 

 Leucite and magnetite (-01) were formed during the first stage, the 

 remaining constituents together with magnetite ('003) during the 

 second stage. 



(7) Olivine-enstatite-augite-picotite rock (Iherzolite). This associa- 

 tion was obtained by prolonged cooling. The artificial product 

 differed from the natural rock in having the picotite in octahedra 

 not in irregular plates. Moreover, glass-inclusions were more abundant 

 in the artificial than in the natural rock. 



(8) Anorthite-augite rock with ophitic structure. Obtained by fusing 

 together one part of anorthite and two of augite, or one part of anorthite 

 to one of augite. 



During the first stage the mixture was maintained under the arrange- 

 ment No. 2 for four days when the anorthite crystallized out ; during the 

 second stage it was maintained for the same length of time under the 

 arrangement No. 3 or No. 4, when the augite crystallized out. 



Arrangement No. 3 produced the structure throughout the mass ; 

 arrangement No. 4 produced it only in the parts most strongly heated, 

 the augite in other parts being in the condition of microlites. Hence 



