INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 437 
The powdered mineral geiatinized with hydrochloric acid even in the 
cold, and was almostinstantly decomposed when warmed with sulphuric 
acid diluted with an equal volume of water, the silica separating for the 
most part in a flocculent form, and enclosing small grains of unde- 
composed mineral, which were left after dissolving the ignited silica. 
One or two hundredths of silica were however retained in solution, 
and were precipitated by ammonia with the oxyd of iron. Two 
analyses of separate portions of the olivine gave as follows, after 
deducting the undecomposed mineral : 
XIil. XIV. Oxygen. 
Say Coa pot aoovccdconcceos 37°18 37°17 == 19°82 
NUECES OR SROB AR A cn omcnorae 39°36 39°68 == 15°87 
HEBOLORY Cs, fo cfaiwniefeisieis)«.e)- »)-1-)- 22°57 22°54 —= 6:10 
99.06 99.39 
If we suppose the 18-0 per cent. of magnesia fouud above to 
correspond to olivine containing 39-5 per cent. of magnesia, we shall 
have 45-5 per cent. of olivine in the rock examined. ‘The silicates 
not attacked by sulphuric acid were decomposed by fusion with an 
alkaline carbonate, and gave as follows : 
: XV. 
PS TNC hoy sient olcheh say ercuacronsbos: suetuacve veils (ana eireae cateiet aan haat tade 49.35 
PAIN A oie RB eicle cus, ete ot ave eacane Bre cia 5 ADS) cuevasfaline Conia elena els 18.92 
PROSE) GF WONG 56450 obon code no bnecaooNoouEOne 4.51 
GATING Spey cteuayars. sieve) det olal sfs. areteia olexe rs cra aqarelspsisrs oO aveieieeeal os 18.36 
IMT OME RTarenrte eae Matte cit alec wiaielo ere otaty aretotatare cata theca: alert 6.36 
ILORS (GUIRENKESD) SAS Aas soubd Layeobaoncoot GoDDbOo 2.50 
100.00 
A crystal of the black cleavable augite from the olivinitic dolerite 
had a hardness of 6.0 anda density of 3.341; its powder was ash- 
gray. Analysis gave, 
XVI. 
STD cuseiaed.0.cie.0 OU aR HD HOD USIG EAL ER ERS oI enipacien 49.40 
PEUMTTATEL Reta et ercislcletisnetelt alk alee aicletetc ele citlarinta 6.70 
GERSE Ung ha Et oho edie ine ys ise De E Ia hcie Wid ate ie Halal 21.88 
WEAR SIA ae teva rte ine yt ie tpl stcta' ss -aye.40'« «icles asia erate 13.06 
PEOLOMY COL VOTE ste) seal of eialo We) che «Vein Pearce eeccees eSB 
Soda with traces of potash ..........00..... 000s sobs 14 
CIES GOR a eS eRE SRO wis as o CHB BN ems onGs Bed Sete -50 
100.11 
In some portions of the dolerite of Montarville, the feldspar is 
