524 Washington — Contributions to Sardinian Petrography: 



second, (B), is from a prominent dike, about 5 km. south of Cu- 

 glieri, cutting trachyte in the steep eastern face of Monte Tuvo- 

 nari, near " 510" on the map (200, IV). This dike is vertical, 

 about one meter and a half thick, striking JS". 20° W., and with 

 finely developed, transverse columnar structure — standing up 

 like a wall of polygonal masonry. It has not altered the tra- 

 chyte at the contact. 



With them are given analyses made by me of three other 

 Sardinian basalts, C representing the basalts of Monte Arci, 

 D one of those of the recent small cones, and E one of the 

 Tertiary sheet basalts. A silica determination of an andesitic 

 basalt from above Fontana Figu gave 50*20 per cent. 



Table III. 



Analysis of Basalts. 



A B 



SiO, 52*40 52*20 



A1 2 0, 15-26 13-20 



Fe 2 3 0-74 1-29 



FeO 8-33 7*91 



MgO 7-45 8-V1 



CaO 7-33 7'95 



Na 2 3-54 3-20 



K 2 0-99 1-01 



H 2 + 0-29 1-68 



H 2 0- 0-06 0-29 



Ti0 2 3-12 2-00 



P 2 5 _.. 0-49 0-24 



MnO ._ 0-08 



NiO 0-06 



c 



D 



E 



52-79 



53-48 



49-00 



16-45 



13-59 



15-63 



2-74 



1-78 



4-03 



6-44 



8-30 



5-00 



5-56 



5-88 



7-86 



6-51 



7*20 



8-16 



364 



4-38 



3-93 



1-21 



1-02 



2-60 



1-02 



0-79 



0-13 



0-21 



0-11 



0-18 



2-64 



2-52 



3*25 



0-39 



0-59 



0-63 



0-06 



_ _ _ _ 



_ _ - . 



0-18 











100-14 99-68 99-84 99'64 100*40 



A. Basalt ("III. 5. 3. 4"). Flow. Near Cuglieri, Monte Ferru. 

 H. S. Washington analyst. 



B. Basalt (III. 5. 3. 4*"). Dike. Monte Tuvonari, Monte Ferru. 

 H. S. Washington analyst. 



C. Basalt (IF. "5. 3. 4 // ). Flow. Uras, Monte Arci. H. S. 

 Washington analyst, this Journal, xxxvi, p. 589, 1913. 



D. Basalt ('TIL 5. (2)3. 4(5)). Flow. Monte Austida. H. S. 

 Washington analyst. 



E. Basalt ((II) III. 5". (2)3. 4). Sheet. Tres Nuraghes, S. E. 

 of Bosa. H. S. Washington analyst. 



The two analyses are very much alike. This is to be ex- 

 pected, as the dike is evidently a feeder for one of the series 

 of flows to which the other basalt analyzed belongs. The only 

 noteworthy differences are the somewhat higher alumina and 



