466 Professor S. J. Shand — A System of Petrography. 



felspars are zonally built), I am for aiming at the highest attainable 

 precision. For completeness we ought to make another boundary at 

 85 per cent of anorthite, for rocks rich in anorthite deserve special 

 recognition just as much as the albitic ones. This is not a new line 

 of division, for it has been customary in the past to distinguish 

 between gabbro and eucrite. 



Putting now the Or-Ab ratio against the Ab-An ratio, we establish 

 a number — which is theoretically twelve but practically only eight — 

 of families within each of our saturation divisions. The general 

 scheme will be the same for each division, as follows : — 



A 



Ab. + Neph. 

 + Sod. + 

 Anal., etc. 



A 



Or. + Leuc. 



In order to indicate the contents of each of these family-compart- 

 ments I shall confine my attention for the present to the holo- 

 crystalline rocks. Divisions are indicated by means of the letters 

 0, S, u, IF, and W, and the "family" names employed in each 

 division show by means of a prefix or suffix the division to which 

 they belong. Thus all names of saturated or oversaturated rocks end 

 in -ite ; those of U-rocks in -oid 1 ; names of u-rocks may carry 

 either the prefix sub- or the suffix -ole ; and for W-rocks the prefix 

 sub- will be used in conjunction with the suffix -oid. "Where a name 

 is put in brackets it is to suggest that a new name is required. 



O 1, granite ; 2, ekerite ; 3, (albite-granite) ; 4, granodiorite ; 5, tonalite ; 

 6, granodolerite ; 7, (quartz-gabbro) ; 8, (?). 



S 1, syenite ; 2, laurvikite ; 3, (albite-syenite) ; 4, inonzonite ; 5, diorite ; 

 6, (orthoclase-gabbro) ; 7, gabbro ; 8, eucrite. 



u 1, subsyenite ; 2, sublaurvikite ; 3, (?) ; 4, submonzonite ; 5, subdiorite; 

 6, (?) ; 7, subgabbro ; 8, subeucrite. 



U 1, (syenoid) ; 2, laurvikoid ; 3, (foyaoid) ; 4, monzonoid ; 5, essexoid ; 

 6, (?) ; 7, theraloid ; 8, eucroid. {Alternatively, U 1, 2, 3, syenoid ; 4, 5, 

 dioroid ; 6, 7, S, gabbroid.) 



W 1, subsyenoid ; 2, sublaurvikoid ; 3, (subfoyaoid) ; 4, submonzonoid ; 

 5, subessexoid ; 6, (?) ; 7, subtheraloid ; 8, subeucroid. {Alternatively, 

 W 1, 2, 3, subsyenoid ; 4, 5, subdioroid ; 6, 7, 8, subgabbroid. ) 



1 Trans. Geol. Soc. Edin., 1910, p. 376. 



