on these rocky shores causes very deep water so that only small amounts
of sand are scoured up from the rocks and deposited on the shores. On
the mainland of West Gloucester, opposite Annisquam village, there are
very extensive dunes which are in active operation, moving farther inland
each year (see Figs. 40, 41), and several tracts of tillage land have been
overwhelmed. Dimes now cover woodlands in this region to a depth of
68 EROSION OF THE SHORE BY WAVE-ACTION
eight to fifteen feet, the sand having been deposited within the past thirty-
years. Drift-sand also occurs at Rockport in the valley occupied by Cape
Pond brook, near the Boston and Maine railroad. Here, also, it is wind-
blown and forms small dimes which are now fast disappearing as the
sand is blown into the brook and carried away. These sands were probably
deposited by the brook in times of flood.
Erosion of the Shore by Wave-Action. — The north shore of Gloucester
from Squam lighthouse to Halibut point, Rockport, is bold and rocky,
and fringes of granite and dike-rock ledges are exposed for nearly the
entire distance. In a small bay back of Davis' Neck, at Bay View, sedi-
ments of sand and mud are deposited, and also at Folly cove, Lanesville,
and at Plum Cove beach. These sediments are clearly derived from till
which partially covers the granite ledges. Sandy Bay, Rockport, is a
deep indentation in the coast-line formed on a line of weakness at a con-
tact of the hornblende granite and the augite syenite rock formations.
At the deepest part of the bay, the incurving shore receives the larger
portion of the sediments produced by wave-action in cutting down head-
lands. On the eastern side of Cape Ann, from Emerson's point to Cape
Hedge, there is now a cobblestone beach. The sand that covered this
beach in 1893, has been dragged into deep water, carried southward, and
deposited on Long]beach, at Gloucester, from thence to be washed along
the shore, for at the present time there is less sand upon this beach than
appeared a few years ago. The same may be said of the beach between
Brier Neck and Bass Rocks, at East Gloucester. Singing Sand beach or
Old Town beach, at Manchester, is also wasting away. The beach de-
rives its name from the rasping sound produced by the sand when it is
walked upon. This sand is peculiar to this beach and the sound is caused
by hard mineral surfaces rubbing against other projecting surfaces. A
microscopical study of sections of this sand has demonstrated that a por-
tion of the grains have rutile needles in and through the quartz and stand-
ing out beyond the surface. In one section these rutile crystals were
found to radiate like the spokes of a wheel. Zircon crystals are also pres-
ent in the feldspars. As the rutile and zircon crystals are harder and
tougher than the feldspars, the grinding together of these grains pro-
duces the sound which gives its name to the beach.
Opposite the Ipswich end of Plum island and between Ipswich river
and Green's creek are the drumlins known as Jeffrey's Neck. Between
the North ridge and Plover hill, the sea has cut a small bay at the mouth
of which a sand-bar has formed, damming the opening into the bay and
Fig. 32.— VIEW FROM GALE'S POINT, MANCHESTER, AT LOW TIDE.
Showing the following islands: House, Misery, Ram, Baker's, Eagle, and Lowell.
Fig. 33. — COFFIN'S BEACH, WEST GLOUCESTER, FROM BLACK ROCKS TO THE LOAF.
Showing ripple marks and cuspated drifting of sand. Ipswich beach and Plum island in the distance.
Fig. 34. — COFFIN'S BEACH, WEST GLOUCESTER.
Showing sand-dunes and Post- Pleistocene or Quaternary drift sand.
I'K-'
dl
^tf^^
w
■s^'^^^^. ^ • ■■<i~.
Fig, 35. — POST-PLEISTOCENE WIND-BLOWN SAND-DUNE AT CASTLE NECK, IPSWICH,
Showing stratification of the sand.
Fig. 36. — IDEAL CROSS-SECTION FROM HOG ISLAND, ESSEX, TO IPSWICH BEACH.
A. Drumlin. B. Kame gravel. C. Clay. D. Sand-dunes. E. Ipswich Beach.
Fig. 37.— POST-PLEISTOCENE WIND-BLOWN SAND OVERWHELMING AN APPLE ORCHARD.
On the Lakeman farm, Castle Neck, Ipswich.
EROSION OF THE SHORE BY WAVE-ACTION 75
making what is now known as Clark's pond. A similar bar tmites Great
Neck and Little Neck at Ipswich. Davis' Neck is connected with Bay-
View, Gloucester, by a sand-bar, and a sand- and cobblestone-bar at Brace's
cove, East Gloucester, encloses Niles pond. Forty years ago. Graves'
island was connected with the mainland at Manchester, but subsidence and
high tides have cut the bar and it has now entirely disappeared. Incipient
bars have formed in the comparatively smooth water on the westerly
side of Eagle, Coney, and Misery islands, in Salem harbor, and a few years
ago Great Misery was connected with Little Misery by such a sand-bar,
but in 1 90 1 the sea had cut a deep-water channel between the islands.
Marblehead Neck is tied to the mainland by a sand and cobblestone beach
(see Fig. 43), and Nahant is connected with Little Nahant by a curved
sand-bar, and beyond, with the mainland at Lynn, by a sand-bar that is
over a mile in length. A small bar at Pond beach, Bass Point, Nahant,
encloses Bear pond. The long bar connecting Little Nahant with Lynn
and all similar bars are called "tombolas," by Italian geologists.^
Nearly all of these bars would be swept away by the sea but for the
work of man in repairing the waste. The sea has frequently cut a pas-
sage through the bar connecting Marblehead Neck with the mainland,
and the beach if not repaired would soon open up a channel and cause
Marblehead Neck to become an island. The same is true of Nahant beach
bar.
' See F. P. Gulliver, Proceedings of A. A. A. Science, 1S99.
CHAPTER III
OUTCROPS OF BED-ROCK
Nearly one half of the bed-rock of Essex County is distinctly strat-
ified, and by means of our knowledge of these groups the geologic age of
all the other rock-masses may be approximated. The term " stratified
rock" is applied to different rock-formations in which stratification is
the only common character, and although the syenites, diorites, felsites,
and some of the breccias show stratification in part, there is little diffi-
culty in separating them from the limestones, quartzites, and argillaceous
rocks.
Stratified Rocks of Sedimentary Origin. — The sedimentary rocks of
the County are nearly all of the Olenellus Lower Cambrian age, and are
divided into several groups: the slates, sandstones, limestones, and the
quartzites, all of detrital origin and to be classed as more or less
metamorphic.
Metamorphism is here used in a broad sense as indicating the produc-
tion of new minerals or new structuresi or both, in pre-existing rock-
masses. An excellent example of thermal metamorphism, due to the
intrusion of volcanic rhyolite rocks, may be seen on the Breakheart Hill
farm in Saugus. The slates here must have contained a considerable
amount of carbonaceous matter, probably due to animal remains, which,
when brought into contact with the great heat of the intruding rhyolites,
were transformed into graphite and produced the knotted-schists or
knottinschieffer of this area. These slates are in part brecciated by the
intrusion of veins and masses of the rhyolite rock, and in some parts of
the slate-beds the metamorphism assumes the type of flaky-schists, with
all the varying gradations between knotted and flaky forms. The slates
and sandstones on Marblehead Neck have been metamorphosed by the
intrusion of veins and masses of hornblende granite, diabase dikes, and
felsitic porhyries. The carbonaceous matter has been transformed into
garnets, and the slates and sandstones have been changed into beds of
quartzite and mica-schist. At Nahant the Cambrian slates have become
-SAND SPIT OFF CASTLE NECK, IPSWICH.
from Hog island, looking across Castle river.
-CONTINUATION OF THE SAND SPIT OFF CASTLE NECK, IPSWICH,
seen from Hog island. Glacial drift boulders appear in the foreground.
Fig. 40 — SAND-DUNES ON A ROCKY HEADLAND NEAR COFFIN'S BEACH.
West Gloucester.
Fig. 41. — SAND-DUNES SOUTH OF COFFIN'S BEACH.
West Gloucester.
Fig. 42.— KAME RIDGE ON SOUTH BANK OF CASTLE RIVER.
North of Hog island, Essex. Ipswich lighthouse and Plum island in the distance at the left.
Fig. 43.— BARRIER BEACH BETWEEN CLIFTON AND MARBLEHEAD NECK.
(July, 1905) showing sea-worn pebbles washed into windrows by the tides.
CAMBRIAN ROCKS 83
calcined into a form of lydite, and andalusite has been developed in the
folia or bedding-planes.
Cambrian Rocks. • — The Cambrian rocks of Essex Coimty are small
remnants of a series of folds which must have been at least 10,000 feet in
thickness. These remnants are now seen at Pickering's point, South
Salem, on the shore at a point northeast of Fort Pickering; at Naugus
head on the Marblehead side of Salem harbor; and northwesterly across
Beverly harbor at the base of Goat hill. As the inclination or dip of these
strata of Cambrian rocks is constant, it being about 40° southeast, the
distance in a straight line across the upturned remnants, from Naugus
head on the Marblehead shore to the outcrop at the base of Goat hill in
Beverly, is about 10,000 feet. These beds probably were continuous
across the area now known as Salem and Beveriy harbors, and formed a
fold at least 10,000 feet in thickness, covering not only Salem and Beverly
but the whole of Essex County. During the Cambrian period there were
mountains of these strata over the igneous eruptive granites and diorites.
A demonstration of the above conclusion was shown at the time an arte-
sian well was sunk on the property of the Salem Electric Lighting Company,
on Peabody street, Salem. This well was bored to a depth of four hun-
dred feet through nepheline syenite and diabase dike rocks. A sufficient
supply of water not having been reached, it was decided to explode a
heavy charge of dynamite at the bottom of the well. The explosion
brought to the surface pieces of Cambrian limestone, one containing
fragments of HyoUthes. By the accompanying diagram (see Fig. 44) it
will be seen that this well is about 5,400 feet from Naugus head. A
similar diagram carrying these strata to the outcrop at the foot of Goat
hill in Beverly, would demonstrate the strata to be at least 10,000 feet in
thickness.
Half-tide rock and Jeggles' island, in the southwestern part of Salem
harbor, are small masses of the harder diorite rock which cut through
the Cambrian slates. Half -tide rock has a vein of syenite cutting through
it. The harbor itself is carved out of the softer Cambrian rocks, especially
those near the contact of the igneous eruptive rocks. At such contacts
invariably there is deeper water than elsewhere in the harbor.
At Jeffrey's ledge, about twenty miles east-northeast from Cape Ann,
a deposit of Cambrian rock has been located, containing numerous fossils
of HyoUthes and Stenotheca, and thereby this outcrop may be connected
with the Olnellus Cambrian deposits of Nahant. Other outcrops of these
crystalline Cambrian sediments have been found in various parts of the
84 CAMBRIAN ROCKS'
County. One at Rowley, chiefly in the valley between Hunslow hill and
Long hill but occasionally rising to an elevation of one hundred feet,
is composed of a series of schistose argillite shales, ferruginous sandstones,
and a cherty limestone which is much metamorphosed in bands of light
and dark color. Microscopical examination shows this limestone to be
composed of plainly stratified sediments of calcite, quartz grains, epidote,
chlorite, some magnetite and limonite, and to be of the same character
as that at Mill cove. North Weymouth. The fossils found at this outcrop,
which can be identified, are all in the cherty limestone. The strike of
this deposit is 20° north of east to southwest, dip 40° west, which is nearly
parallel to the strike of the Olenellus Cambrian deposit at Nahant head.
Another outcrop of these Cambrian rocks is found at Topsfield and is
composed of the same succession of schistose argillite shales, ferruginous
sandstone, and a cherty limestone that is near lydite. Other outcrops
have been found at Archelaus hill in West Newbury, at an elevation of
nearly two hundred feet ; in red argillite shales in the bed of the Merri-
mac river; at Ward's hill in Bradford; and on the high hills of Methuen,
at an elevation of one hundred feet.
The inference to be drawn in explanation of the presence of these
Cambrian deposits scattered over the County is, that during the Cambrian
period there was a vast sheet of these sediments deposited over the entire
region to the depth of some htmdreds of feet; but the great amount of
denudation from various causes, particularly through the agency of the
ice-sheet which covered this region during the Glacial period, together
with the frequent faulting of the strata, makes it nearly impossible to give
the exact depth of these beds. They have been distorted and crumpled
into anticlinal and synclinal folds accompanied by, and perhaps casually
connected with, the intrusion of the granite, diorite, syenite, and felsite
eruptive rocks. The eteolite-syenite of Naugus head, on the Marblehead
shore, and at Woodbury's point, on the Beverly shore, are seen to cut
these sediments, and being also later cut by gabbros and quartz felsites,
the contact metamorphism is so complete that the old crystalline sedi-
ments are now found as mica-schists. The diorite areas of Marblehead
proper, Salem, Danvers, and Ipswich often contain fragments and masses
of these metamorphosed crystalline sediments. At Danvers Centre a
granitic gneiss is found. In Putnamville and Wenham the entire area
is amphibolite schist or foliated hornblende diorite. Mining shafts and
trenches for water-mains have opened these rock-masses in several places,
showing the actual contact. In digging a well at Tapleyville, Danvers,
Fig. 45.— HORNBLENDE EPIDOTE GNEISS CUT BY A COARSE HORNBLENDE GRANITE.
Crooked pond, Boxford.
Fig. 46.— INCLUSION OF HORNBLENDE EPIDOTE GNEISS IN FOLIATED QUARTZ HORNBLENDE
DIORITE.
narrow vein of the diorite cuts through the gneiss upon which the watch is resting. Southeast of Crool<ed pond,
Boxford.
CAMBRIAN ROCKS ' 89
on the bank of Tapley's brook, a bed of typical argillaceous shale was
revealed. This brook occupies the valley between the granite areas of
Peabody on the south, and the main mass of the diorite on the west
and north, and the contact of these eruptive rocks with the crystalline
sediments is probably so distant that the metamorphism in them is less
complete.
In the eruptive dome-shaped bosses of the hornblende granite areas
of Saugus, Lynnfield, Peabody, Manchester, and Cape Ann, there are
numerous fragments and masses of these metamorphosed crystalHne
sediments. At Saugus on the east, and at Lynnfield on the west, of the
granite there are extensive outcrops which are seen to be interstratified
with layers of quartzite and mica-schist. This mica-schist is identical,
macroscopically and microscopically, with the metamorphosed argillites
of Nahant and Flying point, Marblehead Neck. The strike of all these
beds is northeast to southwest, varying only a few degrees either to the
north or east) thus showing that the intrusion of the eruptive magma was
parallel to the foliation of the sedimentary beds. On Cape Ann there
are numerous masses and fragments of the metamorphosed sediments in
the hornblende granite. One large mass, near the Loaf, a rocky point on
the northern end of Coffin's beach. West Gloucester, is several rods in
extent and the foliation shows the strike to be northeast to southwest.
This outcrop is below the high-water line and therefore the dip cannot
well be made out. Another outcrop near Halibut point on the east side
of Cape Ann, is of the same type and has the same strike, with the dip
40° west, parallel to the Cambrian beds at Rowley and Nahant. The
position of these two metamorphosed crystalline sedimentary beds signifies
that they are remnants of an anticlinal fold of the Cambrian sediments,
perhaps produced by the intrusion of the eruptive granite magma from
beneath them. It is not unreasonable to presume that the granite magma
melted and enclosed large masses and fragments of these old Cambrian
sediments, metamorphosing them into hornblende and mica-schist. This
theory will also explain the presence of several gneissic fragments found
in the granite quarries. Such a mass in the Trumbull quarry at West
Gloucester, is twenty feet in length and tapers to a point near the surface
of the dome-shaped granite boss. The enormous force exerted by the
intrusion of the granite magma from beneath upon these Cambrian beds
must have distorted them and left their entire surface a series of faults,
cracks, and crevices, thus exposing them to all the various forces of erosion
and decay. The work of the ice-sheet during the Glacial period must
90 HORNBLENDE EPIDOTE GNEISS
necessarily have been upon these sedimentary beds, scouring and grinding
them to rounded boulders and to fine till, which were deposited all over
Cape Ann and in the waters of the Atlantic. One of these stratified
boulders on Ten Pound island, in Gloucester harbor, and another on
Thatcher's island, are typical examples of the larger of these fragments,
while in Whale cove there are great numbers of all sizes and of every
shape. This theory would also account for the absence of glacial grooves
and striae on much of the surface of the granite areas, for probably the
ice-sheet never touched the larger portion of the granite. Aerial decay
has since destroyed all that was left of these sedimentary beds after the
ice period, except such remnants as are fotuid to-day.
A large number of thin sections from all the outcrops, when studied
with the microscope to determine the detrital character of these strati-
fied beds, have invariably sustained the determinations made in the
field.
Hornblende Epidote Gneiss. — This is an ancient rock-mass, and
probably the oldest member of the Archean series represented in Essex
County. The granitic quartz hornblende diorite, which is the principal
formation in the Crooked pond area at Boxford, and which occurs in both
massive and foliated forms, cuts through the hornblende epidote gneiss.
Veins of granite also cut both of these rocks in various directions. (See Fig.
45.) Nearly half a mile south from the above outcrop, are ntimerous blocks
of this gneiss as inclusions in the foliated and massive quartz hornblende
diorite. (See Fig. 46.) The hornblende epidote gneiss is therefore shown
to be an older formation than the quartz diorite, and it is also demon-
strated that the flow of the quartz hornblende diorite magma, which picked
up the blocks of this gneiss, was from the north in a southerly course, as
there are no outcrops of the gneiss south of the included blocks. A short
distance southwesterly from Crooked pond is an outcrop of this rock in
the form of a conglomerate, a breccia cut by forms of the quartz horn-
blende diorite. Dynamic metamorphism has greatly altered the minerals
in this rock, which has been pressed and crushed between a massive
amygdaloidal melaphyre dike on the east and the quartz hornblende
diorite on the west. In consequence, the augite is nearly aU replaced
by green hornblende which the crushing force exerted was sufficient to
thoroughly metamorphose. The original brown hornblende is replaced
by biotite and the soda-lime feldspars, and the soda-bearing silicates
are separated in the form of crystals of albite, while the lime-bearing
silicates, in conjunction with other constituents of the rock, aid in forming
Fig. 47.— PHOTOMICROGRAPH OF HORNBLENDE EPIDOTE GNEISS.
Crooked pond, Boxford.
-CAVE IN LEDGE OF QUARTZ HORNBLENDE DIORITE.
East of Crooked pond, Boxford.
HORNBLENDE EPIDOTE GNEISS 93
the minerals rich in lime, such as epidote, zoisite, and calcite. These
minerals form narrow elongated lenses, some of which are three or four
inches long and give the metamorphosed rock-mass a distinctly gneissic
appearance, suggesting to some geologists the name — stratified diorite.
A later phase of the metamorphism of this rock is the crushed and broken
crystals of secondary feldspar, which may be seen near the contact of the
aplitic granite veins, which cut through this entire series of melaphyre,
quartz diorite, and hornblende epidote gneiss. North of Crooked pond
this gneiss has been quarried for building purposes. Southwest of the
quarry there is an outcrop of this rock in the form of a conglomerate
of rounded pebbles, which becomes a breccia still further in the same
direction.
South of Woodchuck hill, on the north side of Boston brook, there
is an outcrop of the hornblende epidote gneiss with a strike northeast
to southwest. Continuing in this course about two miles, the rock again
appears on the Jenkins farm in Andover. Northeast from the first out-
crop, it is also seen south of Fish brook, near the North Andover and Box-
ford town lines. South of Kimball and Sawyer's mill-pond in Boxford, a
series of outcrops extend nearly to Four Mile pond, and west of the first-
named pond a gneissic quartz diorite is found. On both sides of the
outlet to Stiles' pond, and on either side of Spofford's pond, are outcrops
of hornblende epidote gneiss. Southwest of Rock pond in Georgetown,
there are three outcrops.
On the bank of Mill river, at Dodge's mill, Rowley, this formation
appears, and in a northeasterly direction there are numerous outcrops.
Two hundred yards southwest from the Mill river outcrops, a blue lime-
stone appears, beyond which is another outcrop of the gneiss, and then an
outcrop of foliated quartz hornblende diorite.
On the south side of Uptack hill in Groveland and extending eastward
to "Federal City," are several outcrops of hornblende epidote gneiss,
which reach southward and appear on both sides of Rock pond in George-
town. Half a mile north of Bald Pate pond is another outcrop in a rail-
road cutting, and at the southeastern base of Long hill, at "Rooty Plain,"
are two other outcrops between which appear blue limestone and quartzite.
The strike of the whole series is north 40° east, the dip varying from 30°
north of west to 90°.
Following the strike of the hornblende epidote gneisses across Essex
Cotmty, there are outcrops in various places near Foster's pond, Andover,
and on the roadside, in a cutting near the John Jenkins farm, there is an
94 ANCIENT ROCKS OF SEDIMENTARY ORIGIN ON CAPE ANN
exceptionally good exposure where this gneiss is seen for several rods
with the same strike and with the dip slightly to the west. Numerous
exposures are also seen in Famhamville, North Andover, and on the Lacy
farm on the road to East Boxford.
Hornblende epidote gneiss from Crooked pond (see Fig. 47); section across
the bedding, microscopic structure: green hornblende; twinned feldspar with numer-
ous inclusions of quartz grains; patches of quartz in which there are numerous
fluid inclusions; large patches of zoisite, biotite, and magnetite; numerous areas of
chlorite and epidote. Section parallel to the bedding shows the zoisite surround-
ing hornblende crystals and the hornblende in turn surrounding grains of magnetite,
all lying in one plane across the section dependent upon one plane of pressure.
Titanic iron surrounded with leucoxene is abundant in this section.
A section across the bedding of a specimen of metamorphic hornblende epidote
gneiss from the John Jenkins farm, Andover, gave brown hornblende allied to
green hornblende ; magnetite ; plagioclase with numerous inclusions of quartz ;
biotite flakes, and masses in the plane of bedding ; numerous quartz grains, many
of them well-rounded and containing numerous fluid inclusions ; some patches of
chlorite ; numerous grains of epidote ; a little sahalite, and large masses of zoisite.
Ancient Rocks of Sedimentary Origin on Cape Ann. — The principal
and largest mass of this sedimentary rock is seen on the shore at the west-
erly side of Folly point, east of Langford's cove, at Lanesville. This
outcrop varies in width from ten to thirty feet. The strike is north 40°
east to southwest. The length of the outcrop, exposed between low
water and the covering of drift on the hillside, is about one hundred yards.
The microscopic structure is : well-rounded grains of quartz and feldspar, scales
of biotite, some titanite, garnets with irregular outline, and some magnetite. The
larger feldspars have inclusions of muscovite, quartz, and epidote, and are sur-
rounded by chlorite. This rock is clearly a mica-schist, metamorphosed from a