^30 Canadian Record of Science. 



of nepheline in the former. In this rock, however, it is 

 very difficult to distinguish the nepheline from the feldspar 

 in every case. These discrepancies indicate that in apply- 

 ing Eosiwal's method to comparatively coarse-grained 

 rocks such as these, especially if there be any tendency 

 to irregularity in composition, a considerable number of 

 thin sections should be employed in order to obtain a true 

 average of the rock as a whole. 



For purposes of comparison the analysis of the essexite 

 from Shefford Mountain (No. Ill) has been reduced to its 

 normative form and the position of the rock in the 

 Quantitative classification determined. It is found to be 

 as follows : 



Class II, dosalane. 



Order 5, germanare. 



Rang 3, monzonase. 



Subrang 4, akerose (grad = polmitic). 



It thus, in composition, occupies, in a manner, a middle 

 place between the essexose and andose of Mount Johnson. 



The Pulaskite. — This soda-syenite which, as above 

 mentioned, forms the outer zone of the mountain, girdling 

 the essexite, is less abundant than the latter, and differs 

 greatly from it in appearance. This difference is due 

 chiefly to the fact that it is much lighter in color, being 

 pale-yellow or buff instead of dark-gray, the lighter color 

 being due to the very small proportion of iron-magnesia 

 constituents present and the marked preponderance of the 

 feldspars. The rock also has a more massive structure, 

 the fluidal arrangement of the constituents often met 

 with in the essexite being absent, and it weathers in a 

 somewhat different manner. It possesses, moreover, a 

 species of porphyritic structure, owing to the development 

 of the feldspar in two forms ; first, as stout prisms, up to 

 10 mm in diameter, which are light-gray in color and very 

 abundant ; and, secondly, in the form of smaller laths of a 

 yellow or buff color which, in association with the iron- 



