THE PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 799 
more basic specimens, such as one from the railroad cut just north 
of the Manchester station, would correspond to them. The 
rather high lime is to be noted, but this is used up in the forma- 
tion of pyroxene, leaving none for lime-soda feldspar, which, as 
the microscope shows, is not present. 
Nordmarkite (mica-hornblende-quartz-syenite ).— In Shaler’s 
geological map of Cape Ann’ there is indicated on both sides 
of Squam River an area of igneous rock, which is called diorite. 
Sears,? after a careful study of all the occurrences, came to the 
conclusion that they are not diorite but ‘phases of the augite- 
syenite rock,” an opinion in which I concur. These rocks 
are far more limited in their distribution than the preceding, 
being found chiefly in Shaler’s ‘‘diorite”’ area in West Gloucester 
and along the Squam River. I have specimens also from Hos- 
pital Point, Beverly, and from Salem Neck. They are light- 
gray fine-grained rocks, of granitic structure, looking like 
fine-grained diorite, composed of a white mass of feldspar, with 
subordinate quartz, thickly sprinkled with black specks of 
biotite and hornblende. The specimens from Hospital Point 
and Salem Neck are porphyritic through the presence of rec- 
tangular feldspar phenocrysts, from five to ten millimeters in 
length, and a few small quartzes. 
They show under the microscope a granitic structure, though 
the quartz is less apt to be interstitial and usually forms small 
rounded spots in the feldspars, but is not pegmatitic as in the 
micrographic granite. The feldspars are alkali-feldspars, but 
do not show much tendency to microperthitic intergrowth. For 
the most part they are orthoclase or soda-orthoclase in simple 
crystals or Carlsbad twins. Albite is present in smaller amount, 
showing fine twinning lamella, with the extinctions proper to that 
mineral. In the specimens from Shaler’s ‘ diorite ”’ area biotite 
is almost the only colored constituent. It forms small brown or 
greenish-brown, strongly pleochroic flakes, which are only rarely 
altered at the borders with development of magnetite grains. A 
*SHALER, 9th Ann. Rep. U.S. G. Surv., Pi. LX XVII, 1889. 
2 SEARS, Bull. Essex Inst., Vol. XXV, 1893. 
