REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r63 



minerailogic and chemical characters of the rock in the different 

 areas agree so closely as to afford strong presumption of their 

 essential unity. Granting the unity of the rock, it must then be 

 all classed with the anorthoelte as a member of series 3 of 

 Kemp's classification. The granites also, the one due to yariation 

 in the syenite mass, the other of somewhat later origin, must be 

 included in the same series, which thus comes to include a great 

 group of eruptive rock^ ranging from acid granites, through 

 jsyenite and anorthosite, to quite basic gabbros. 



One objection to the above view which has often impressed 

 itself on the writer is that the syenites and granites are more 

 frequently and more markedly gneissoid than are the anortho- 

 sites, thus preeenting the appearance of having experienced more 

 excessive metamorphism than has fallen to the lot of the 

 anorthosite, and therefore implying a greater age. But it is 

 believed that this difficulty is more apparent than real, and likely 

 is due to the peculiar character of the anorthosite magma. The 

 great deficiency of iron and magnesia in this, which gives the 

 rock its character as a purely feldspathic one with nearly total 

 freedom from dark silicates, is probably responsible for its 

 unusual coarseness of crystallization, and prevents much recrys- 

 tallization as a result of metamorphism^, at least recrystallization 

 can only give rise to more feldspar. All three rocks anorthosite, 

 syenite and granite, show much variation from place to place,, 

 being here quite massive and there well foliated, and the more 

 massive syenites and granites show clearly that they never 

 possessed any approximation to the very coarsely crystalline 

 character of the anorthosite. Therefore they would granulate 

 more readily and would show small, rather than large augen. 

 Whenever the anorthosite shows any tendency toward gabbro, 

 ^ark silicates appearing in any amount, the grain becomes lesa 

 coarse, foliation appears and recrystallization also, notably shown 

 by the abundance of garnet. The more purely feldspathic 

 syenites also are apt to be coarser than those in which the iron 

 and magnesia percentages are higher. 



