GEOLOGY OF MOUNT MARCY 53 



to think that the bostonite dike at the head of Johns brook came 

 from some ledge in the immediate neighborhood. 



Prof. Albert B. Leeds, in connection with the analyses of anor- 

 thosite and its constituent minerals earlier referred to, also made an 

 ?nalysis of one of the basaltic dikes, named by him dolerite, and 

 stated to be intrusive in the'Norian rocks (that is, anorthosites, as 

 we now use the term). Doctor Leeds also examined a thin section 

 and has given us the following microscopic description (pages 28- 

 29 of the separate). From it we can do little more than conclude 

 that the specimen came from a very dense, and presumably narrow 

 dike, and that it probably was a camptonite: 



21 Section of the dolerite, whose analysis has been previously given. A 

 large portion of the transparent base of this rock could not be definitely 

 referred by its optical characters to plagioclase. It presents a considerable 

 admixture of quartz. The dark color of the section and rock is due in part 

 to the magnetite and menaccanite, but in still greater degree to very minute 

 light to dark green and yellowish-red masses. The former are probably 

 pyroxene, the latter, which are by far the most abundant, hornblende. 



Doctor Leeds unfortunately does not give the locality whence the 

 specimen was obtained. The rock with its high CO2 and HoO was 

 obviously not perfectly fresh, although some of the water may have 

 been in analcite. All the water was in a soluble mineral, but it 

 seems strange that some of the silica did not also go into solution. 

 In so basic a rock, the quartz, if correctly determined, must have 

 been secondary. In citing the analysis and its two associates the 

 oxides have been rearranged somewhat, to conform with modern 

 customs. 



Total Soluble Insoluble 



SiO. 

 TiOo 

 AUO., 

 Fe^Os 

 FeO 

 MgO 

 CaO 

 NasO 

 K2O 

 CO. 

 H2O 



Sp. gr. 



If we attempt to recast the analysis we can not assign all the NaaO 

 to albite because then we will run short of SiO, for the anorthite, 

 which must be in so basic a rock in even greater quantity than the 

 albite. On the other hand, if we assume that the NaoO is in analcite 

 or nephelite in sufficient proportion to ease the difficulty just stated. 



43-41 • 





43-41 



0.35 



0.367 





19.42 



9.097 



10.324 



5-72 



4.553 



1. 169 



6.69 



6.693 





5. 98 



5.285 



0.695 



^.11 



7.398 



1. 711 



4-39 



0.530 



3.864 



0.47 



0.323 



0.144 



2.00 



2.003 





3.00 



2.997 





100.54 



39.246 



61.317 



2.89 







