GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 523 



cannot be absolutely affirmed; indeed it may be only partly 

 due to assimilation and largely to the fact that the process 

 of differentiation which produced the great segregation 

 veins containing nearly pure albite, to be discussed in the 

 succeeding part of this paper, impoverished the main rock 

 near these veins (which is all that is accessible) in regard 

 to the albite component ; so that the average composition 

 of the plagioclase of the pallio-essexite would be only a 

 little more acid than that of the original magma before 

 intrusion, and that of the main rock distinctly more basic. 

 Hence we may say that there is evidence of slight assimil- 

 ation, but no more. 



Analyses of Prospect and other rocks. 

 Table I. 





I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 











(Prospect) 







Si0 2 



47-45 



46-92 



45-41 



43-06 



41-05 



47-90 



47-00 



A1 3 3 



14-83 



18-05 



16-85 



16-31 



12-27 



16-55 



15-20 



Fe 2 3 



2-47 



3*61 



4-14 



5-40 



639 



5-67 



5-69 



FeO* 



14-71 



6-73 



8-86 



7-90 



11-26 



8-10 



6-85 



MgO 



5-00 



7-43 



7-27 



5-49 



6-38 



444 



8-76 



CaO 



8-87 



9-11 



9-43 



9-37 



1096 



9-35 



12-60 



Na 2 



2-97 



2-99 



3-38 



3-12 



2-43 



3-23 



1-45 



K 2 



0-99 



1-24 



0-64 



1-07 



0-53 



2-08 



0-66 



H 2 



1-00 



2-58 



2-63 



4-09 



402 



0-2 



030 



co 2 



0-36 



010 



0-09 



1-36 



003 







Ti0 2 



1-47 



0-94 



1-41 



2-46 



439 



1-91 



2-30 



P 2 5 





0-19 



018 



0-32 



0-19 



0-32 



trace 





100-12 



99-98 



100-29 

 Tabl( 



100-30 

 3 II. 



100-31 



99-75 



100-81 





I. 



II. 



III. 



IV. 



V. 



VI. 



VII 



Si0 2 



48 



48 



46 



46 



43 



48 



47 



Al 2 O s 



15 



18- • 



17- 



17- 



13 



17 



15 



Fe 2 3 



2-5 



3-7 



4-3 



5-5 



6-7 



5-7 



5-7 



FeO* 



15 



7 



9 



8- 



12 



8 



7 



MgO 



5 



7- 



7- 



6 



6- 



4- 



9 



CaO 



9 



9- 



10 



10 



11- 



9- 



12- 



Na 3 



3 



31 



3-5 



3-3 



2-5 



3-3 



1-5 



K 2 



1-0 



1-3 



•7 



1-1 



•5 



2-1 



•7 



Ti0 2 



1-5 



10 



1-5 



2-6 



4-5 



1-9 



2-3 



P 2 6 





•2 



•2 



•3 



•2 



•3 



trace 



* To the FeO are added MnO, NiO, and CoO. 



