278 



FRANK D. ADAMS- 



The Structure of Motmt Jolmson. — The structure of the moun- 

 tain and the character of the rocks composing it also throw 

 some light on the question as to where the differentiation took 

 place. In course of conversation with the foreman of one of the 

 quarries in the essexite on the flank of the mountain, the writer 

 was informed by him that Mount Johnson consisted of three lay- 

 ers of horizontal rock; a fine-grained one on top, below which 



Fig. 5. — Quarry in andose, Mount Johnson, showing vertical flow structure on 

 right. 



was the coarser-grained rock of the quarry, and beneath this a 

 spotted variety. Each of these layers, he considered, went through 

 the mountain horizontally and could be seen outcropping at their 

 respective levels on every side. The three rocks referred to 

 were, as will be recognized, the fine-grained essexose, the 

 andose, and the transitional rock below the latter, respectively. 

 The pulaskite zone he had not noticed, it being at the base of 

 the mountain and in many places more or less covered with fallen 

 blocks and talus. If this were the true interpretation of the 

 structure, the mountain would have to be considered as the rem- 



