470 PROF. W. S. BOT7LTON ON A MONCHIQ.UITE LNTETJSIOX [Nov. 19TI,. 



IY. Chemical Composition. 



An analysis of the rock l has been made by Mr. Sydney J. John- 

 stone, of the Imperial Institute. It is given below, with some 

 others for comparison : — 



Si0 o 



Ti0 2 



A1.,0 3 



Fe'O" 



Fe 2 3 



Cr 2 3 



V 2 0, 



MnO 



(CoNi)O 



BaO 



CaO 



MgO 



K„0 



Na o 



*A 



so 3 



s 



FeS 2 



co 2 



CI 



H 2 Oatl05°C. .. 

 H 2 above 105° C 



Totals 



I. 



Per cent. 

 4026 

 226 

 10-22 



714 



2-86 

 trace 



O20 



13-43 

 8-75 

 1-32 

 1-51 

 0-65 

 0-62 



5-80 

 trace 

 1-24 

 3-53 



99-7' 



II. 



Per cent. 

 39-54 



2-72 



13-74 



7-85 



4-05 



0-40 

 0-05 

 019 

 9-64 

 8-66 

 3-70 

 224 

 1-01 



027 

 2-48 



6-61 



2-77 



99-92 



III. 

 Per cent. 



4222 

 2-49 



10-62 

 6-18 

 474 

 010 

 0-05 

 0-50 

 005 

 004 



14-80 

 8-68 

 1-41 

 2-46 

 073 



612 



357 



6-50 

 1-16 



100-42 



IV. 

 Per cent. 



44-01 

 2-03 



1232 

 8-75 

 362 

 trace 



0-21 



trace 



10-57 



12-86 



0-49 



1-68 



0-17 



o-'ii 



trace 



6-89 

 2-73 



10044 



Per cent. 



42-46 



2-47 



12-04 



534 



319 



0-16 



undet. 

 12-14 

 12-40 

 2-68 

 1-21 

 0-84 

 none 



0-55 

 none 



4-03 



99-51 



I = Monchi quite near ' Great House,' Golden Hill, Monmouthshire. (Anal. 

 S. J. Johnstone.) 

 II = Nepbeline-ouachitite, Kilchattan, Colonsay. (Anal. E. G. Radley.) 

 ' The Geology of Colonsay & Oronsay, with part of the Ross of Mull' 

 Mem. Geol. Surv. Scot. 1911, p. 46. 

 Ill = Camptonite, Sailean Sligenach, Ardmucknish, Argyllshire. (Anal. 

 E. G. Radley.) See ' The Geology of the Country near Oban & 

 Ualmally ' Mem. Geol. Surv. Scot. 1908, p. 126. 

 IV — Olivine-dolerite, Ciche na Beinne Deirge, Skye. (Anal. W. Pollard.) 

 See ' The Tertiary Igneous Rocks of Skye ' Mem. Geol. Surv. 1904, 

 p. 325 ; also ' Geol. of Colonsay, &c.' op. supra cit. p. 46. 

 V = Monchiquite, Willow Creek, Castle Mountain district, Montana (Weed 

 & Pirsson, Bull. U.S. Geol. Surv. No. 139, 1896, p. 115). (Anal. 

 L. V. Pirsson.) 



The specific gravity of the Monmouthshire rock is 2'85. It has 



1 In selecting material for the analysis, care was taken to exclude, as far as 

 possible, xenoliths of Old Bed Sandstone and picrite. As shown on p. 473, 

 fragments of the latter would not appreciably affect the result ; while the 

 former, if present, would have the effect of slightly raising the percentage of 

 silica and alumina. 



