A CONTRIBUTION TO THE GEOLOGY OF SOUTHERN MAINE 549 



basicity, the analysis was a surprise, and so was the position of 

 the rock in the quantitative system. It falls into the same 

 rang as a rock from Southport which in the field was considered 

 a granite. Microscopic examination leaves no doubt that the 

 analysis is correct, the black color being deceptive. 



Microscopic Characters. — Thin sections show the rock to have 

 a normal diabasic texture; to be of coarse grain, and to lack 

 phenocrysts. The edges are finer than the center. The prin- 

 cipal constituent is plagioclase, appearing as a network of lath- 

 shaped crystals. The extinction angles of these were measured 

 and they were found to be of two kinds : one corresponding to 

 albite of the composition ab6 ani, the other oligoclase, ab3 ani. 

 A microperthitic intergrowth of albite and orthoclase is of oc- 

 casional occurrence, and one interesting type of intergrowth 

 was seen, where laths of albite alternated with strips of micro- 

 perthite. A fine dust of kaolin is to be seen in some of the 

 feldspars. A few broad orthoclases are present. Anhedra of 

 magnetite are common, occupying the interstices between the 

 feldspars. The principal ferro-magnesian constituent is common 

 augite which is entirely xenomorphic, consisting of long strips 

 or of irregular areas between the feldspar laths. The augite is 

 entirely fresh and without inclusions. 



Table XL 

 Analysis and Norm of Placer ose from Dike near Sheepscot River. 



Composition. 



Molecular 

 Proportions. 



Norm. 



Si0 2 



56.72% 



•945 



Qu 



10.56 



A1 2 3 



15.06 



.148 



Or 



3-89 



Fe 2 3 



i-73 



.010 1 



Ab 



39.82 



FeO 



6 -33 



.088 



An 



18.07 



MgO 



2.58 



'.064 



Diop 



9.98 



CaO 



6.61 



.118 



Hyp 



5.88 



Na 2 



4-73 



.076 



Mag 



2.32 



K 2 



.69 



.007 



Ilm 



7-55 



H 2 + 



•5i 





Ap 



.98 



H 2 0- 



•15 









co 2 



none 









TiO 



4.04 



.049 







P 2 O s 



.40 



.003 







MnO 



•35 



.004 







Total 











99.91 









