276 W. S. Bay ley — Sod a- Granite, etc., of Pigeon Point. 



teristic features would be those of a plutonic rock, since the 

 conditions under which it solidified (as shown bj the nature of 

 the contact phenomena) are those that give rise to the distinc- 

 tive features of plutonic rocks. The porphyritic structure 

 noted in a few places must be due to local conditions that pre- 

 vailed only at a few localities. Under this assumption are 

 explained the intrusion of the keratophyre into the slates, the 

 crumpling of the latter and the alterations effected in those 

 near the sides of dykes of the former, and in fragments in- 

 cluded within its mass. 



The distribution of the red rock, its occurrence only between 

 the gabbro and the altered quartzite, is the strongest argument 

 in favor of its secondary origin. A glance at the map will 



Fig. 1. — Geological Sketch Map of Pigeon Point. Scale 1 in. = about \\ miles. 



show that the red rock occurs only in areas lying between 

 the gabbro and the members of the contact belt.* At no 

 other places is it found, except in the form of dikes directly 

 connected with the larger masses of the rock. If it can be 

 shown that the contact rocks owe their origin to the presence 

 of the gabbro near them, it will follow as a natural proba- 

 bility that the red rock is likewise of contact origin. Where- 

 ever it exists there is on one side of it the gabbro and on the 

 other side two or more members of the contact belt. Its 

 position is that of a member of the contact belt. It follows 

 the sinuosities of the gabbro as no irruptive rock would be 

 likely to do, and is present in greater or less amount according 

 as the contact belt beyond it exhibits contact phenomena in 

 greater or less degree. Where this contact action has + been 

 most intense there is found the greatest amount of ttie red 

 rock ; where the action has been less in degree the amount of 



* In consequence of the small scale upon which the map is drawn only the zone 

 of most intense alteration is represented on it. The outer zones of the contact 

 belt extend along the entire southern edge of the gabbro and the red rock, 

 throughout all that portion of the point represented in the map. 



