260 



width from less than three feet to more than thirty feet on 

 Herscv Street. In the end of the lane the outcrop of diabase 

 measures 100 feet north and south ; and the southern extension 

 appears the best explanation of this fact. The east-west 

 branches are, possibly, indejiendent and intersecting dikes. 

 Certainly the main or more southerly branch east of Hersey 

 Street presents striking characters not observed in the others. 

 Its eastern outcrops in the sandstone, where it is from 6 to 7 

 feet wide, are very distinctly and quite coarsely porphyritic, 

 enclosing feldspars one fourth of an inch long. It is also very 

 hio'hly magnetic, containing a large amount of magnetite in 

 grains up to half an inch or more in diameter. Farther north 

 Hersey Street is crossed by two parallel dikes 3 feet and 8 

 feet in width ; but east of the street they are smaller and 

 appear to unite and then divide again ; while west of the street 

 they seem to be offshoots from a large mass of trap of 

 undetermined form. The other dikes call for no special 

 comment. Where the width is not given on the map, it 

 means that the outcrop is unsatisfactory ; and several dikes 

 have been omitted for this reason. Evidently, the dikes of 

 this area are especially characterized by their irregular, 

 branching forms, which makes it unsafe to map them beyond 

 their outcrops. 



Dikes of the BeaVs Cove Area. 



Tiiis part of Ilingham appears to be comparatively free from 

 dikes ; the only one distinctly represented on the map being the 

 irregular ten-foot dike at the mouth of Beal's Cove. This 

 a})pears to belong to the south-of-east system ; but its trend may 

 mean nothing more than a natural tendency to follow the bedding 

 of the slate. About 1,000 feet directly east of the northern 

 arm of the cove, on the south side of Tucker's Swanij), a large 

 mass of trap breaks through the conglomerate and sandstone, 

 which was inadvertently omitted from the maj). It is impos- 



