GEOLOGY OF THE NORTH CREEK QUADRANGLE 



29 



seeming to conform to no law. . . , These primary variations in 

 the rock suffice to give considerable diversity to different portions 

 within a limited area, but this diversity is greatly intensified by cer- 

 tain secondary modifications of structure and composition. As a 

 result of the combined effect of primary and secondary variations, 

 it would be easy to collect, within an area of a few square rods, a 

 half dozen or more specimens whose appearance even in thin section 

 would scarcely suggest that they had any connection with one an- 

 other." Gushing says ^ of the Adirondack gabbros in general that 

 they show much variation, both primary and secondary, from place 

 to place. Both of these investigators proceed to discuss the sec- 

 ondary variations and their causes but, so far as the writer is aware, 

 little or no attention has been given to the causes of the primary 

 variations which will be considered below. 



Microscopic features 

 Mineralogical composition. The following table will serve to 

 show the great range in mineralogical composition of the gabbro 

 and its derivatives. The figures refer to percentages by volume and 

 are meant to Ije close approximations only. 



TABLE 4 

 Mineralogical composition of the gabbro and its derivatives 





d 

 ."2 



4) 

 f. 



"o 

 



X. 

 ^- 











(/! 



"0 







'5b 



n! 



T3 

 C 

 _4J 



3 



c 



u 







4> 

 C 

 H) 



X. 



in 



u 



0, 



>> 



'Ei 

 < 



0) 



t 



(5 



'S 



g 



l-H 



'C 



a, 







(5 



c 



<A 

 



)-■ 



a 



"55 

 '0 



c5 







a 

 < 



c 

 



Titanite 



T 



45 



6 



2 



46 



42 



47 



I 



60 



5 



49 



3 



4 



44 



43 



4.5 

 15 

 10 

 10 



5 

 20 



32 

 32 

 15 

 50 



45 



Lab. 50 

 Lab. 50 

 01-Lab. 38 

 Lab. 30 

 01-Lab. 40 

 01-Lab. 30 

 01-Lab. 40 

 01-Lab. 40 

 01-Lab. 4S 

 01-Lab. 10 

 01-And 20 

 01-Lab. 57 

 01-Lab. 15 

 01-And IS 



8 

 27 

 10 



?5 



:fi5 



17 



12.5 



15 



3 



7 



23 

 10 



3 



I 



2.5 



5 



little 

 I 

 I 

 I 

 2 

 2 

 5 

 2 



little 

 I 



little 



I 



little 



I 



I 



little 



I 

 little 

 little 



9 



8 



7 

 5 



I 



2 



5 



2 

 6 

 6 

 5 

 10 



8 



8 



3 • S 











15 





7 













^ 









little 







1 



20 

 little 

 2 

 8 

 10 

 2 

 5 













s 















6 



25 

 16 

 10 



14 

 45 

 25 

 15 

 20 

 28 



r2o 



' 25 



1 14 

 1 20 































8 



























10 







little 



'little 

 little 









T I 









10 





little 





little 



12 











r { 





8 

 2 



2 





I 



8 





little 

 little 







1,1 























Perhaps the most striking feature brought out by this table is the 

 range of rock types, through many intermediate phases, from a 

 very basic olivine norite to (|uartz-hornblende syenite. Thus, no. i 

 is an olivine norite; nos. 2, 3, 4, 6. 7, and t; arc hornblende norites ; 



\N. V. State Mus. I!ul. ';5. p. 32S. 



