626 



FRANK D. ADAMS 



alteration of some constituent which has now entirely disappeared. 

 As will be seen, the rock has the composition of an ordinary clay 

 slate, possessing the characteristic high content of alumina with a 

 low percentage of alkalis and a great preponderance of magnesia 

 over lime, which is characteristic of these rocks.' 



No. I 



SiOs 61.96 



TiO^ 1.66 



AI.O3 19.73 



Fe,0, 



FeO 4-6o 



FeSz 



MnO Trace 



CaO-... 35 



BaO 



MgO 1. 81 



Na^O : 79 



K2O 2.50 



P.O5 



Graphite Not det. 



Water i . 82 



No. II 



79-7° 



30 



8.29 



41 



117 



4.33 Not det. 



03 



67 



08 



76 



1-43 



411 



04 



3-00 



70 



99-55 



100.69 



No. II is from the township of Stanhope in the Haliburton area 

 and is distinctly different in composition. If the "Mode" or per- 

 centage mineral composition of this rock be calculated, it is found 

 to be as follows : 



PEE CENT. 



Quartz ■ - 55 



Orthoclase 18 



Oligoclase 14 



Biotite 3 



Muscovite 3 



Rutile 



Apatite 



Calcite 



Graphite 3 



Water 



99 



I See F. D. Adams, "A Further Contribution to our Knowledge of the Lauren- 

 tian," American Journal of Science, July, 1895. 



