60 lloyal Society : — ■ 



No. 4. Callernish, extreme west of Lewis. In metamorphie Gra- 

 nite ; in large grey crystals, with a slight shade of pink, translucent. 

 The oxygen ratio of these felspars is as follows : — 



No. I. No. 2. No. 3. No. 4. 



Silica 33-956 33-456 33-478 33*477 



Alumina &c. .. 8-898 8*950 9-348 9*348 



Lime 0-061 0*187 0*286 0*221 



Soda 0*929 0*699 0-440 0-56 1 



Potash 1-908 2-059 2-171 2-051 



45-752 45-351 45723 45-65S 

 From this Table we find the oxygen ratios : — 



No. 1. No. 2. No. 3. No. 4. 



Silica 11-37 11*35 11-55 11-82 



Peroxides 3-06 3*04 3*22 3*30 



Protoxides .... l'OO 1-00 1-00 TOO 



The Granites of central and western Scotland are metamorphie 

 rocks, like those of Donegal and Norway, with which they are geo- 

 logically identical ; and truly eruptive Granite occurs at only a few 

 localities, as, for example, near Peterhead. 



The second felspar associated with Orthoclase in the Metamorphie 

 Granites is Oligoclase, as in Donegal ; while the second felspar asso- 

 ciated with Orthoclase in the eruptive Granites is Albite, as in 

 Mourne, Leinster, and Cornwall. The fact thus indicated by the 

 Scotch Granites is completely in accordance with the mode of 

 occurrence of Oligoclase and Albite in the Irish Granites. 



II. Oligoclase. 



No. 1. No. 2. 



Silica 62*00 61-88 



Alumina 23-20 24-80 



Magnesia trace. 



Lime 471 4-93 



Soda. 9-20 8-12 



Potash 0-43 0'98 



99-54 100-71 



No. 1. This Oligoclase occurs in the Granite of Craigie-Buckler, 

 near Aberdeen ; it is white and opaque, and so much resembles 

 Cleavelandite in appearance as to have been mistaken for that variety 

 of Albite ; its analysis proves it to be Oligoclase. The crystals do 

 not exhibit striation. 



No. 2. From the Granite of llhiconich, in the west of Sutherland- 

 shire ; it is greyish white, semitranslucent, in large striated crystals, 

 and resembles the Oligoclase of Ytterby, in Sweden. 



