90 GEOLOGICAL AND MINERALOGICAL NOTES. 



ardite and napoleonite. These iiames would bring them 

 into the diorite group, but their composition proves them 

 to be forms of the syenite, which is as distinct from the 

 diorite as the diorite is from the granite. On the Beverly 

 shore the syenite is cut in various directions by recent 

 dykes of feldsite and diabase, and at Hospital Point, Bev- 

 erly, on the east side, there is a peculiar form of dyke 

 called a laccolite, one of which has been described by 

 Mr. G. K. Gilbert. It was discovered in the Henry mouu- 

 tains in sonthern Utah and consists of large bosses of lava, 

 which have risen from beneath, but, instead of finding their 

 way to the surface, have spread out laterally and pushed 

 up the overlaying strata, giving it a somewhat dome- 

 shaped appearance. 



The main rock-mass of Salem Neck is diorite, com- 

 posed of oligoclase, feldspar and hornblende. The acces- 

 sory minerals as seen by the microscope are calcite, biotite, 

 apatite, orthoclase, grains of quartz, magnetite iron, lim- 

 onite, zircon crystals and chlorite. Most all of these are 

 alteration products of the hornblende. This diorite as- 

 sumes various forms in different places even in the same 

 strike and dip, the strike being N. E. to S. W., and the 

 dip 60° N. W. In places on Salem Neck, it is composed 

 of large patches of hornblende and oligoclase feldspar with 

 magnetite iron. In other places it is largely hornblende 

 and again oligoclase. Some of it is very finely and evenly 

 mixed and again it is seen strongly porphyritic, with large 

 crystals of the oligoclase feldspar, and in some scctions 

 it becomes quartz diorite, but this I think is due to the 

 granite, with which it is associated, as I have only ob- 

 served it in places where the hornblendic granite was 

 closely joined to the diorite. 



It has been stated that the sodalite on Salem Neck was 

 found in drift-boulders. This is clearly proved to be in- 



