72 



J. A. Dresser — A Rare Rock Type. 



rock. The writer in a recent examination, the results of which 

 will be published in a report to the Geological Survey, did not 

 rind any part of the rock so rich in olivine as that, but fonnd 

 olivine commonly present up to 25 per cent, as well as could 

 be judged by the eye. The rock is dark greenish black or brown 

 in color. Pyroxene, olivine, biotite, sometimes feldspar and 

 usually specks of pyrrhotite can be distinguished in it by the 

 unaided eye. It is an even-grained, plutonic rock having a 

 rather coarse texture. 



In the thin section it is found to be composed essentially of 

 pyroxene, olivine, brown hornblende, biotite, and labradorite. 

 The hornblende and biotite are often intergrown with each 

 other and sometimes with the pyroxene. The accessory min- 

 erals, pyrrhotite, titanite and apatite, are in their characteristic 

 positions with the earlier constituents. The general order of 

 crystallization has, therefore, been — olivine and accessories ; 

 pyroxene ; hornblende and biotite ; feldspar. A fresh speci- 

 men, which did not represent the maximum content of olivine 

 seen, was taken and submitted for analysis to Mr. M.F.Connor 

 of the Geological Survey, Ottawa, Canada, who gives the fol- 

 lowing results in column I : 



SiO„ 45 



A1 2 3 ._.. 6 

 Fe 2 3 .... 2 



FeO 8 



MnO._... 

 NiO + CoO 



MgO 18 



CaO 14 



NaO 



K,0 .._.. 



co 2 



Ti0 2 1 



HO 



•37 

 •21 

 •40 

 •09 

 •15 

 •17 

 •67 

 •47 

 •85 

 •37 

 •62 

 •50 

 •88 



PA + FeS, 



II 

 39-97 



8-68 



8-63 



7-99 



•19 



1-11 



10-32 



15-18 



1-19 



•74 



1-15 



4-05 



•57 



III 



48-63 



5-32 



2-91 



3 90 



•12 



•21 



21-71 



13-04 



•34 



•23 



•47 

 2-81 



IV 



49-02 



10-14 

 1-54 



1046 

 0-16 

 0-11 



17-25 

 8-29 

 1-59 

 0-40 



0-99 

 0-75 



99-75 99-89 100-13 100'70 



*I Palisadose, St. Bruno Mt., Quebec, M. F. Connor, analyst. II Yamas- 

 kose (yamaskite) Mt. Yamaska, Quebec, G. A. Young, analyst. Ill Bel- 

 cherose, Belchertown, Mass., L. G. Eakins, analyst. IV Palisadose 

 (olivine diabase) Englewood Cliffs, N. J., B. B. Gage, analyst. 



Calculating the molecular ratios in Analysis I and reducing 

 these to percentages of standard minerals, the norm is found 

 to agree so closely with the estimated mineralogical composi- 

 tion of the rock that it may be safely considered a normative 

 rock. 



