GEOLOGICAL AND MINERALOGICAL NOTES. 119 



cline-microperthite. The outcrop of this augite-syenite, 

 in the marsh near the poor farm, used by the city of Glou- 

 cester for road making, is of a very dark color and a 

 macroscopical examination would indicate it to be diorite, 

 but the microscopical structure, as seen in thin sections, 

 shows it to be composed of augite, segirine, hornblende, 

 limonite, some biotite, orthoclase, microcline-micioper- 

 thite, zircons, apatite, magnetite and a little quartz as a 

 cement in theground-mass, thus making the rock atypical 

 augite-syenite. Numerous thin sections have been pre- 

 pared from all parts of the outcrops of this augite-syenite 

 described above. In specimens from the corner of War- 

 ner and Prospect streets in the city of Gloucester, the mi- 

 croscopical structure is quite characteristic of this rock 

 mass. They all contain augite, aegirine, titanite, micro- 

 cline-microperthite with some quartz. Some of the sections 

 contain nepheline and one section contains an excess of the 

 fine multiple twinned albite (sp. gr. 2.63). There is more 

 or less orthoclase, hornblende, biotite and magnetite with 

 crystals of zircon and apatite as inclusions in the feldspars, 

 showing this rock mass to be a nearly typical augite-syen- 

 ite. 



From the area mapped as diorite (9th Annual Keport 

 of the United States Geological Survey : Geology of Cape 

 Ann by Prof. N. S. Shaler) in Gloucester and the Islands 

 in Squam river, I have collected specimens from every 

 outcrop. These have been carefully studied and compared 

 with known types of the augite-syenite group from other 

 parts of the region and, after making thorough micro- 

 scopic analyses of numerous thin sections, I am convinced 

 that these outcrops are phases of the augite-syenite rock. 

 The microscopical structure, when studied from thin sec- 

 tions in polarized light, shows these outcrops to be com- 

 posed of augite-syenite minerals, microcline-microperthite 



ESSEX INST. BULLETIN, VOL. XXV 17 



