Vol. 62.] 



CATARACTS OF THE RIVER MADEIRA., ETC. 



117 



of which is given in colunm (a) of Table XIV of the ' Quantitative 

 Classification of Igneous Hocks ' Chicago, 1903. 



Percentage j; Ortho- Am 



Mineral \ clase. 



Composition J 4219 11-05 



Si0 2 ! 27-32 7'59 



A1 2 3 1 774 2-15 



Fe 2 3 ! .... s ... 



FeO 



MnO 



MgO 



CaO 



K o 713 ... 



Na 2 .., ... 1-31 



TiO, 



p 2 o; - 



F 



H 2 0(eombined) ... 

 Less O re- 

 placed by F 



Anorth- 

 ite. 

 0-89 



038 

 0-33 



0-18 



j Quartz. 

 I 38-79 



38-79 



4219 11-05 089 I 3879 



Bio- 



Fluor. 



Apat- 



tife. 





ite. 



6-89 



0-09 



011 



2-48 







1-30 







0-39 







1-02 







0-06 







0-68 







0-04 



0-06 



0-06 



0-64 







0-03 







008 







... 





6-05 



0-02 



0-04 



trace 1 



0-18 





... 



-001 



-0-02 



... j 



6-91 



0-08 



011 , 



Percentage 



Chemical 



Composit. 



100-02 



76-56 



11-52 



0-39 



102 



0-06 

 0-68 

 0-34 

 7-77 

 1-34 

 0-08 

 0-05 

 006 

 0-18 



-0-03 



1000: 



An analysis was subsequently made of this rock by Mr. G. S. 

 Blake, with the folloAving result : — 



SiCL 





Percentage 

 composition. 



... 73-96 



Molecular 

 proportions 



1-2351 



Ti0 2 





trace 





ALO, 





... 13-10 



01284 



Fe CL 





074 



0-0046 



FeO 

 MnO 

 MgO 

 BaO 

 SrO 





.... 1-28 

 .... 004 

 .... 0-18 

 .... 06 

 013 



00178 

 0-0006 

 00045 

 00004 

 00013 



CaO 

 K 2 





.... 0-70 

 5-05 



00125 

 0-0537 



Na 2 





3-55 



0-0573 



p 2 o. 





0-102 



00007 



s 



F ... 





.... 0041 



0-084 



0-0013 

 0-0044 



H 2 Oat 

 H 2 Oa 

 LessO 



)ovel00°C 



tioo°c 



replaced by F.. 

 Total 



.... 0-930 

 .... 0-230 

 .... -0036 



0-0517 





... 100141 





These figures correspond fairly well with the calculated com- 

 position, except in the case of the alkalies. The total molecular 



