

102 



characters of the mica have boon already described. Tho hornblende is 

 pale green by transmitted light, and shows a pleochroism which is characteristic 

 but not strongly marked. Sometimes it contains tabular inclusions, which 

 have suggested to Professor JUDD that it may have boon derived from diallage. 

 Sorpentinous pseudomorphs occur in the hornblende, and their characters are 

 llms described by Professor JUDD : "Examined with high powers of tho 

 microscope, this serpentine is seen to be filled with black and brown 

 enclosures, some rod-like and stellate in form, others of a tabular character. 

 Sometimes these inclusions are arranged in one set of parallel planes only ; in 

 other cases they lie in two sets of planes intersecting one another. There can 

 he no doubt that much of this serpentine is pseudomorphous after olivine ; 

 but some of it may replace enstatite." The relative proportions of the 

 different materials have been estimated by making a number of drawings 

 with the camera lucida and then cutting out and weighing the portions which 

 represent the different minerals. The result obtained by Professor JUDD is 

 as follows: 



Hornblende . . . . 58 '5 per cent. 



Serpentine . . . . . . 22'0 



Altered mica . . . . . . 18*5 



Magnetite and accessory constituents I/O 



The chemical composition of the rock is given in the following table 

 of analyses. 



ANALYSES OF 151UTISH AND FOREIGN ROCKS BELONGING TO GROUP A. 

 I. II. III. IV. V. 



Si0 2 ... 42-80 ... 43-84 ... 45-68 ... 39-103 ... 40-79 



ALO, ... ... 1-14 ... 6-28 ... 4-940 ... 10-41 



Cr.,() : , ... ... 0-42 ... 0-2C ... -44(5 ... 



Fe.0 a ... I ( 4-315 ... 3-52 



FeO ... 9-40 ) " " ( 11-441 ... 6.39 



CaO ... ... 1-71 ... 2-15 ... 3-951 ... 8-48 



MgO ... 47-38 ... 44-33 ... 34-76 ... 29-176 ... 23-34 



MnO ... ... -12 ... ... -276 ... 



K a O ... ... ... ... tr. ... 0-71 



Xa 2 O ... ... ... ... ... 1-71 



H s Onii(lCO s '57 ... 1-06 ... 1-21 ... 5-669 ... 4-04 



Kio-15 101-38 99-4G 99-:! 17 99-39 



S]>. (Jr. 3-290 8-287 8-20!) 2'93 2-960 



