THE STRATIFIED ROCKS OF ESSEX COUNTY. 33 
which have been idoiitified by Mr. Charles D. Walcott of 
the United States Geological Survey, Washington, D. C. 
The strike of this limestone is 18° noithof east, the dip 
40^-43° west. 
In the month of July, 18U0, I discovered an outcrop of 
this Olenellus limestone in a valley between Prospect Hill 
and Hunslow's Hill in Rowley. It has nearly all become 
altered to chert and epidote, but fragments of the Hyo- 
litlies fossils are still to be found in it. j/ 
This outcrop dips under a red sandstone which in turn 
is covered with the fine grained granitic gneiss of the re- 
gion. The strike of this newly discovered outcrop cor- 
responds very nearly with that of the Nahant rock of 
similar character, and is 20° north of east with a dip 45° 
west. A mass of diorite, known as Metcalf's rock, cuts 
across this limestone on the southeast near the Ipswich 
line and on the north it is covered by the banded red fel- 
sites of By field. 
Near Bennett's Head, Nahant, the strike of this lime- 
stone is 20° west of north, dip 45° southeast. Here the 
limestone rock mass has been turned or pushed one side by 
the intrusion of a massive llyke of very unusual character, 
and which under the microscope in thin section is seen to 
be composed of hypersthene, olivine somewhat serpen- 
tinized, diallage, i)lagi()clase, biotite, numerous brown zir- 
cons, magnetite, a little calcite and brown hornblende. 
At a short distance north of Bennett's Head, Nahant, 
there is exposed at low tide a metamorphic schist having a 
strike northeast to southwest. It is again seen at Bass 
Point in the southwest part of the town. The microscopic 
structure of this schist in thin section is : grains of quartz, 
some feldspar in bands alternating with dark bands com- 
posed of grains of quartz, grains of magnetite in large 
amount, flakes of biotite, some flakes of chlorite, muscovite 
ESSEX INST. BULLETIN, VOL. XXII 3 
