202 MR. H. II. THOMAS ON THE [May IQTI, 



still more acid than they should be in a normal basaltic rock. 

 There is no doubt that these basic mugearites pass gradually into a 

 group of olivine-basalts which have well-defined fluxion-structure 

 and a general absence of phenocrysts. Of these more basic mugea- 

 rites I may mention rocks from south of the Flagstaff, Skoiner 

 (E 7767, Analysis IX, below), and from just above the sediments 

 in South Haven (E 7014). 



IX. X. XI. XII. 



SiO., 50-10 40-24 40-20 50-06 



TiO; 2-72 184 2-27 24(5 



Al o 3 14-57 1584 1666 15-72 



Fe;d, 430 600 724 394 



FeO° 896 748 4'81 7*63 



MnO 032 020 055 0"30 



(CoNi)O notfd. ... 0-04 003 



BaO O-03 000 ... 003 



CaO 7-60 5-26 563 5'90 



MgO 270 302 2-42 382 



K 2 1-53 210 186 216 



Na 2 4-24 5-21 4-08 455 



Li 2 trace ... ... notfd. 



H.X>atl05°C 0-32 1-08 034 0'67 



H.;0 above 105° C... 154 161 2-11 1-36 



P.,0-, 112 147 024 064 



FeS. 003 ... ... nt. fd. 



CO.; 0-02 ... 232 1-08 



CI " O05 ... ... 0-04 



F ... 018 



S ... 0-03 



100-42 ... ..: 10039 



Less O for CI 001 ... ... 0*01 



Totals 100-41 ... ... 100-38 



Anal E. Gr. Eadley. W. Pollard. W. Pollard. E. G. Kadley. 



IX=Mugearite (lava) ; south-east of the House (Skomer). [Analysis No. 346. 

 Slide E 7767.] 

 X=Mugearite (intrusion) ; Skye. [Analysis No. 263. Slide S 13250.] 

 XI=Mugearite (lava) ; quarry, Corston Hill, Corston (Midlothian). [Ana- 

 lysis No. 247. Slide S 12710.] 

 XII=Mugearite-basalt (lava) ; hilltop, half a mile north-east of Balhennan, 

 9 miles south-west of Stirling. [Analysis No. 338. Slide S 14130.] 



As regards mineral constituents and chemical composition, the 

 rocks of this group compare quite well with the mugearites of 

 Mr. Harker, and therefore they have been classed as such, although 

 there is little doubt that the Skomer rocks are extrusive and not 

 intrusive like the mugearites of Skye. 



It wiil be seen from the analysis of the somewhat basic 

 mugearites (E 7767) that the felspar is on the labradorite side 

 of true oligoclase, and in this respect the rock approximates to the 

 basalts ; but in all other characters, such as the high percentage of 

 iron-ores, the low percentage of magnesia, and the fairly high 

 percentage of phosphoric acid, it compares well with the type. 



