The Monteregian Hills. 



23T 



The transition rock. — : As has been metnioned, there 

 intervenes in Mount Johnson between the pulaskite 

 border and the central mass of essexite a transitional zone 

 consisting of a * ,0 » 



rock which is dark 

 in color and thus 

 resembles the es- 

 sexite, but which 

 is characterized by 

 the presence of 

 large porphyritic 

 feldspars sometimes 

 as much as two 

 inches in length, of 

 peculiar form scat- 

 tered through it and 

 often arranged with 

 their larger axes in 

 the same direction, 

 thus giving a nuidal 

 appearance to the 

 rock. This rock 

 contains a large 

 proportion of the 

 same iron-magnesia 

 minerals, more es- 

 pecially the horn- 

 blende, found in the 

 essexite, and passes 

 over gradually into 

 this rock. Its passage into the pulaskite is rather more 

 abrupt and is marked chiefly by the almost entire 

 disappearance of the dark-coloured constituents above 

 mentioned. There is, however, a continuous transition or 

 passage from the pulaskite through this intermediate rock 

 into the inner essexite of the mountain. 



Fig. 4. — Diagrammatic representation of 

 the chemical composition of the several rocks 

 described. 



No. 1. Laurvikose — Mount Johnson. 



No. 2. Laurvikose— Shefford mountain. 



No. 3. Nordmarkose--Shefiford mountain. 



No. 4. Andose — Mount Johnson. 



No. 5. Essexose — Mount Johnson. 



No. 6. Andose — Shefford mountain. 



