served and very characteristic. On the Asteracanthion, the latter form
large and dense clusters around all the spines, and they are unusually
acute. The same appears in your fossils. The major ones are very large,
1 Leda-clay fossils collected by the author. The first thirteen species were found
in the clay-pit off Liberty street, Danvers. Number fourteen was found at Lynn,
(i) Portlandia Arctica, Gray. (8) Macoma Baltica, Linn.
(2) Pandora clidrophora, Gouldiana, Dall. (9) Modiolaria discors, Loven.
(3) Lyonsia arenosa, Morch. (10) Modiolaria Imvigata, Gray.
(4) Portlandia Iticida, Lroven. (n) Haminea solitaria, Say.
(5) Saxicava Arctica, Linn. (12) Cylichna oryza, Stimpson.
(6) Schizoporella hyalina, Linn.'? (13) Mactra polynyma. Stimpson.
(7) Schisoporella hyalina. vav. Danversiensis, (14) Asteracanthion Lincki, Muller, and
370 SUMMARY OP SUBSIDENCE AND ELEVATION
ovate, sub-acute, especially along the adambulacral plates, but also many
on the dorsal surfaces as in your examples. Dorsal plates are very delicate
and form a slender network. Adambulacral spines are small and slender,
tapered, acute, and a large tubed spine stands singly back of every 4th
or 5th plate (sometimes 3d or 4th) as in yours. In all of these characters
and others, it differs from A. vulgaris. A. stellionura I first took off
Cape Sable, Nova Scotia, on the American side, in 1877. It was abun-
dant in 30 to 60 fathoms, some of them growing to be over two feet
across. It is a very arctic species, common at Spitzbergen and the north-
em Norwegian coasts. This discovery is of much interest."
From the fact that living specimens of these fossils are to be dredged
from the bottom of the sea at the present time, at a depth of thirty to
sixty fathoms, and that all or nearly all are arctic forms, it is fair to pre-
sume that these fossils now found at about sea-level formerly lived at
a depth of sixty fathoms on the bottom of the glacial sea.^ Such assump-
tion would indicate that the surface of the land was formerly three hun-
dred and sixty feet lower than at the present time, a subsidence which
would cause all of Essex County and Eastern Massachusetts to sink be-
neath the sea. Raised sea beaches that were formed as the land was
elevated may be found at intervals across the whole of Essex County,
and toward the northwest into New Hampshire wherever sand-plains
and gravel ridges occur. The sand-plains at Ipswich, Rowley, Byfield,
Georgetown, Groveland, Lawrence, and Methuen mark various raised
beaches where the waters of the glacial sea stood for a time as the country
was being elevated, and this inland sea of subsidence will account for
the water-worn and rounded pebbles underlying the sand-plains, show-
ing them to be ancient sea beaches. It also accounts for the water-dressed
surfaces of many outcropping ledges where the debris of erosion has-
been removed, leaving the bare and rounded exterior. Although the
longer axes of these ledges are parallel to the line of glaciation for the
region in which they occur, there are many examples in all parts of
the County where the surface seemingly has been denuded by sea-action in
recent times and yet exhibits no attendant features that would account
for the presence of the sea at this elevation.
Summary of Subsidence and Elevation. — "The typical and common
species of Yoldia Arctica [the Portlandia Arctica heretofore mentioned]
* During the summer of 1905, the author found in the leda clay-pit on Liberty-
street, Danvers, a nearly perfect valve of a species of Thracia, measuring 17 mm. long and
12 mm. wide.
Fig. 203. — LONGHAM BASIN, NORTH BEVERLY.
Showing escarpment at tlie right and in the background.
Fig. 204. — GRAVEL-PIT AT LEGG'S HILL, SALEM, SHOWING KAME GRAVELS.
RECESSION OF THE ICE-SHEET 373
live in abundance in the high arctic seas at depths from about ten to
thirty meters [96 feet]. A number of high arctic species Uve at greater
depths. The fauna of the younger Portlandia clay comprises partly
the same species as the older, but in other varieties some new forms have
also supervened. Thus, for instance, Portlandia Arctica in the older clay
reaches a length of twenty-seven to twenty-eight mm. ; in the younger
only about eighteen mm. Further, it is to be remarked that this clay
must have been deposited at some greater depth than the older clay, as
is indicated by the change in the fauna." '
The Portlandia Arctica which is the older form, and now collected
at Portland, Maine, and Montreal, Canada, and whose length is 27 mm.
to 28 mm., accordingly must have lived on the sea bottom during the early
part of the Champlain subsidence when the land had been depressed not
more than one hundred feet. Portlandia lucida, Loven, according to
Professor Brogger, occurs in the younger area clays or deep-water forms
at a depth of at least two hundred and forty feet, together with Portlandia
Arctica in its largest forms, i.e., 8 mm. to 14 mm. The P. Arctica and
P. lucida found in Essex County, therefore, are forms that probably
lived on the leda-clay when the subsidence was from 240 to 360 feet in
depth. The yotmger Portlandia clay as deposited was covered up in
the Terrace period by the brick clays, sands, and gravels.
Recession of the Ice-Sheet. — During the closing era of the great ice
period in the Quaternary age the whole of Essex County was submerged
beneath the sea. Even the highest ledges and the tops of the drumlins
were beneath this waste of waters which is now known as the Champlain
Sea of Subsidence. The land surface sank at least three htmdred feet.
As the surface was again elevated, the waters of this sea when disturbed
by storms formed lines of breakers which produced well-defined beach
ridges of gravel and sand. All debris was washed from the summits of
outcropping ledges and drumlins, many of which were channeled and
left thickly strewn with large boulders.
Post-Glacial erosion may be seen in many parts of the County. In
the western part of Georgetown the Parker river has cut a passage to the
sea through numerous ridges and sand-plains, and this is true of all the
streams in the County. The Merrimac river with each recurring spring
season cuts into the bases of the drumlins along its course, and carries the
debris to the delta at its mouth. A fine example of such erosion may be
> Professor W. G. Brogger: Glacial Fauna of Norway and Late Glacial and Post-
Glacial Changes of Level in the Kristiania Region.
3 74 RECESSION OF THE ICE-SHEET
seen at North Beverly, north of Dodge street, where Longham brook has
cut a channel in a sand-plain for a distance of nearly a mile, leaving an
escarpment from fifteen to twenty feet in height. Corrosion has widened
the valley, which in the adolescent stage of the stream was grassed over
and probably covered with forest trees. The Salem and Beverly Water
Boards took advantage of this escarpment and ancient stream-cutting,
and by building a dam created an artificial lake known as "the Long-
ham basin," which serves the purpose of an auxiliary water supply. (See
Sea-worn gravels with round cobble-stones are a general feature of
gravel-beds about the County. (See Fig. 204.) These gravels contain
calcitmi lime in solution, which, when gravel-beds are opened, becomes
carbonized, and cements the small particles of gravel together in a form
of conglomerate, and often produces a crust on the outside of pebbles
and boulders. The presence of this lime indicates that there may have
been shell-bearing moUusks in the gravel and that the shells have been
dissolved by carbonic acid percolating from the surface. Occasionally a
large boulder is found in these gravels, having been dropped from the
bottom of floating ice.
Fig. 205. — PORTLAND/A ARCTICA, GRAY.
From the Peabody Pottery clay-pit, Purcliase Street, Da
Ti(^\ E-Klci\cte(. |!V0-\Ai. ^■\-\uMv\.6\VC.t'^'V^'»^*-^"^'^'
Fig. 206. GLAQAL MARINE FOSSILS FOUND IN LEDA-CLAY IN THE EDWARD
CARR BRICK CLAY-PIT, LIBERTY STREET, DANVERS.
No. I. Portlandia Arctica, Gray, a typical specimen of the largest size, iij mm. long
8 mm. wide.
Nos. la and ib. Portlandia Arctica, Gray, greatly enlarged, showing hinge area with
teeth ; la, upper hinge ; ib, lower hinge.
No. 2. Pandora olidrophora, Goiildiana, Dall., 23 mm. long, 15 mm. wide.
No. 3. Modiolaria discors, Loven., 10 mm. long, 6 mm. wide.
No. 4. Saxicava A?-ctica, Linn., 23^ mm. long, 11 mm. wide.
No. 5. Lyonsia arenosa, Morch., 19 mm. long, 11 mm. wide.
No. 5a. Mactra luteola, Loven., ? in a clay stone.
No. 6. Cylichna oriza, Stimpson, 4J mm. long, 2^ mm. wide.
No. 7. Hamijiea solitaria, Say., 2 mm. long, ij mm. wide.
No. 8 Schizoporella hyalina, Linn., cluster 3 mm. long, 3 mm. wide.
No. 9. Schizoporella hyalina, var. Danversimsis, Sears, elongated colony, i,\ mm. lono-
PALEONTOLOGY OF THE CAMBRIAN ROCKS
Numerous markings in the limestone at East point, Nahant, were
discovered in 1887, by the author, and for the first time considered to be
fragments of fossils. The geologists of Massachusetts did not coincide,
even after a piece of the limestone had been ground to a flat surface and
polished, and the fossil fragments thickly scattered over the surface had
been closely inspected. The polished specimen was then placed in the
geological cabinet at the museum of the Peabody Academy of Science
in Salem. In 1889, Dr. Aug. F. Foerste, the eminent paleontologist,
then a student at Harvard University, collected a series of these fossils,
and published a paper in the Proceedings of the Boston Society of Nat-
ural History (Vol. XXIV, pp. 261-263), in which he identified the species
discovered in 1887 as HyoUthes inequilateralis , a type distinct from Hyo-
Uthes princeps. The name inequilateralis was not generally accepted for
the species, and princeps, Billings, has been assigned. Since 1889 the
author has collected several himdred specimens and fragments of fossils
in the Cambrian limestones at Nahant, many of them being new to Essex
County, and all of which are now preserved in the geological cabinets of
the Peabody Academy of Science. For a detailed accotmt of the fossils
shown in Fig. 209, with the exceptions of Scenella and Fordilla, the reader
is referred to a paper by Dr. A. W. Grabeau on the "Paleontology of the
Cambrian Terrenes of the Boston Basin," published in " Occasional Papers
of the Boston Society of Natural History," Vol. I, part III, pp. 605-656.
Dr. Grabeau received the fossils used in the preparation of his paper with
the understanding that his material should also be available for this work.
Outcrops of Cambrian fossiliferous limestone occur on the extreme
outer portion of East point, Nahant, where the fossil horizon occurs from
ten feet above mean sea-level and extends twelve feet up the face of the
cliff. The beds are interstratified limestone, slate, and chert — an im-
pure quartzite. Here fossils of HyoUthes, several species of brachipods
and Stenotheca, have been found. Another outcrop of this fossiliferous
limestone occurs on the ocean side opposite "MaoHs Spring," so-called,
Fig. 207. GLACIAL MARINE FOSSILS JFOUND IN LEDA-CLAY AT DANVERS.
No. I. A cleavage piece of clay with fossil Portlandia Arctica in position on the natural
bedding of the clay. Reduced \. From the Peabody Pottery clay pit, Purchase street,
No. 2. Modiolaria lavigata, Gray, on a clay stone ; length, 28 mm., width, 26 mm. From
Edward Carr's clay pit. Liberty street, Danvers.
No. 3. Macoma Baltica, Linn., on a clay stone ; length, 23^ mm., width, 23^ mm. From
Edward Carr's clay pit, Liberty street, Danvers.
384 PALEONTOLOGY OP THE CAMBRIAN ROCKS
where HyoUthes princeps occurs, specimens measuring four inches long
and one inch across the basal section having been collected. Still another
outcrop occurs on the Lynn harbor side of Bass point, where the beds are
all below high tide or sea-level. The horizon is about eighteen inches
thick, from top to bottom. This outcrop is near the causeway leading
from Little Nahant to Bass point in a bank by the roadside. The fossils
at this locality are Lower Cambrian and are largely HyoUihellus micans,
Billings ; Stenotheca abrupta, Shaler and Foerste ; Scenella Rohinsoni, Sears
(the latter species named for John Robinson of Salem) ; Orthotheca cylin-
drica, Grabeau; and HyoUthes impar, Ford.
Beside Rowley Bridge street, Topsfield, on the Peterson farm, there
is a series of outcrops of slate, blue limestone, chert, and ferruginous
quartzite. In the limestone and the reddish slates are found fossil casts
of an annelid, 4 mm. in diameter and 30 mm. in length. The blue lime-
stone, which is probably Middle Cambrian, contains numerous minute to
microscopic fossil lamellibranch shells and a sponge, Ethmophyllum, having
only six septa. Ford's specimens have from eighteen to twenty-one septa.
In the roadway east of Archelaus hill, West Newbury, occurs a series of
outcrops of red limestone, slate, and quartzite. The limestone contains
numerous fragments of HyoUthes and other Cambrian fossils. On the west
bank of Batchelder's brook, east of Clay lane in Rowley, there is another
outcrop of Cambrian rocks where the surface is nearly all a chert, which
contains fragments of HyoUthes. While digging a well at the Daniel's
wagon factory at Chaplinville, Rowley, a ledge was encountered which
proved to be a red slate interstratified with limestone from which broken
pieces of HyoUthes fossils were taken. Outcrops of this series of Cambrian
rocks may be seen on both sides of the Boston and Newburyport turnpike
at various points between Chaplinville and Glen Mills. The city ledge in
South Lawrence is also a fossiliferous Cambrian rock of metamorphosed
limestone interstratified with quartzite and slate. In a railroad cutting at
the base of Paper Mill hill in West Peabody there are outcrops of chert,
limestone, and slate, identical in character with the Cambrian fossiliferous
rocks of Nahant, and although fossils have not as yet been discovered,
without doubt the outcrops are of the Cambrian period. On the south side
of Chestnut street, Lynnfield Centre, are numerous outcrops of white quart-
zite, blue slate, and limestone, which contain fossils, probably species of
annelids and fucoids, which Dr. Grabeau was unable to identify. These
outlying outcrops have not been examined critically, and a knowledge
of their fossils is confined to a very hasty inspection.
Fig. 208. CAMBRIAN FOSSILS FROM NAHANT AND JEFFREY'S LEDGE.
No. 2. Hyolithes princeps, Billings.
No. 2a. Dorsal side of a young individual showing forward curving strise and lip.
No. 2b. Fragment of a specimen showing dorsal side and cross-section. Enlarged.
No. 2C. Cross-section referred to this species obliquely cut. Enlarged from 10 mm. to
No. 2d-e. Sections of large specimens from outside of Maolis spring, Nahant.
No. 2f-h. Various cross-sections, the variations in outline being due chiefly to obliquity
of cut. Enlarged.
No. 3. Hyolithes excellens, Billings.
No. 3a. Dorsal side of specimen described. Natural size.
No. 3b. Cross-section of same.
No. 3c. Cross-section of a specimen of this species. Natural size.
No. 4. Hyolithes Americamcs, Billings.
No. 4a. Dorsal view of the specimen described. The upper part is broken away.
No. 5. Hyolithes Sea?-si, Grabeau.
No. 5a. Cross-section of the largest specimen known. Natural size.
No. 5b. Group of cross-sections. Natural size.
No. 6. Hyolithes communis, Billings. Cross-section showing normal form.
No. 7. Hyolithes impar. Ford.
No. 7a. Normal shell with oval cross-section. Enlarged.
No. 7b. Fragment (restored) with cross-section. Enlarged.
No. 7C. Cross-section, enlarged.
No. 8. Orthotheca cylindrica, Grabeau.
No. 8b. Fragment of a large specimen. Enlarged.
No. 8d. Cross-section of the invaginated specimens. Enlarged.
No. 8g, Small curved specimen which may be of this species. Enlarged.
No. g. Orthotheca Emmonsi, Ford.
No. ga. Dorsal view of a specimen showing faint concavity. Natural size.
No. 9b. Characteristic cross-section.
No. gc. Cross-sections of invaginated shells.
No. gd. Ventral view of a specimen with cross-section.
No. 12. Hyolithelhis micans, Billings. A fragment referred to this species from a red
limestone boulder at Nahant. Boston Society of Natural History, Cat. No. ii,g66.
No. 13. Longitudinal section of a hyolithid (?J showing two septa. From blue limestone
at Jeffrey's ledge. Enlarged.
No. 14. Longitudinal section of an undetermined shell. From blue limestone at Jeffrey's
No. 15. Longitudinal section of a Salterella (?). From blue limestone at Jeffrey's ledge.
388 PALEONTOLOGY OF THE CAMBRIAN ROCKS
Recent experiments with a weak solution of muriatic acid upon the
white limestone from East point, Nahant, resulted in etching out perfect
specimens of Stenotheca abrupta, Foerste and Shaler; Ohellela crassa, Hall;
Orthotheca cylindrica, Grabeau ; Hyolithes princeps, Billings ; Hyolithes Amer-
icanus, Billings; Hyolithes Searsi, Grabeau; Hyolithes commtinis, Billings;
Hyolithes impar, Ford, and an interior valve of Fordilla Troyensis, Walcott.
Two very perfect casts of shells of Stenotheca, with six corrugations, have
been found. They are nearly vertical. One measures 4 mm. across the
base and 3 mm. in height, and has been provisionally named Stenotheca
abrupta, Shaler and Foerste, variety N ahantiensis . The second measures 3
mm. across the base at its narrowest part, and is 3 mm. in height. This
shell has been named Stenotheca abrupta, Shaler and Foerste, variety
Foerstei, in honor of Dr. Aug. F. Foerste, the first to describe species of
fossils in the County. A specimen of Hyolithes has been found resem-
bling Hyolithes princeps, Billings, but the cross-section is in the form of a
sexta and entirely different from the Billings type. This shell has been
named Hyolithes princeps, Billings, variety Pingreei, in honor of Mr.
David Pingree of Salem, Mass.
The more siliceous limestone on the Lynn harbor side of Nahant, when
similarly treated, resulted less successfully, for the acid destroyed the
fossils, and usually left only casts. However, this limestone has produced
in abundance minute to ordinary specimens of Hyolithes micans, Bill-
ings, and Orthotheca- cylindrica, Grabeau, of large size and in considerable
n-umber. One piece of cherty limestone contained three nearly perfect
specimens of Hyolithes communis, Billings; and another, a doubtful speci-
men of Hyolithes princeps and a Stenotheca without corrugations. The
dark blue limestone from the outcrop in Topsfield is so homogeneous on
a freshly broken surface that it is impossible to discern recognizable spe-
cies of fossils. These only may be noted in sections ground thin enough
to permit light to pass through the specimen, when numerous fossils
are revealed in every piece of the stone. These fossils comprise minute
brachiopods, lamellibranch shells, fossil sponges, Hyolithes, etc.
Fig. 209. CAMBRIAN FOSSILS FROM TOPSFIELD AND NAHANT.
No. I. Longitudinal section of an Ethmophylhim rarui/i, Ford. From the blue lime
stone on the Peterson-Towne farm, Topsfield.
No. 2. Cross-section of an Ethmophylluui rarum, Ford. Showing six septa. From
No. 3. Cross-section of an Ethiuophylhim, with septa crushed and broken. From same
No. 4. Section of the shell of a species of lemellibranch. From same locality.
No. 5. Section of the shell of a species of lemellibranch, showing hinge area cut
obliquely. From same locality.
No. 6. Section of the shell of a species of lemellibranch, showing the hinge. From
No. 7. Section of the shell of a brachiopod ?. From same locality.
No. 8. Cast of an annelid boring? From same locality.
No. 9. Shell of Orthotheca cyliiidrica. From white limestone, Lynn harbor side of
N ah ant.
No. 10. Shell of Stenotheca abrupta, Shaler and Foerste ? Forma Nahanti, Sears.
From white limestone, East Point, Nahant.
No. II. Shell of Stejiotheca abrupta, Shaler and Foerste? Forma Foerstei, Sears.
From white limestone. East Point, Nahant.
No. 12. Cast of shell of Stenotheca abrupta, Shaler and Foerste. From white limestone,
Lynn harbor side of Nahant.
No. 13. Cast of shell of Scenella Robinsoni, Sears. From Lynn harbor side of Nahant.
No. 14. Scenella varians, Walcott. From white limestone. East Point, Nahant.
No. 15. Fordilla Troyensis, Walcott. Cast of the interior of the right valve enlarged.
From white limestone, East Point, Nahant.
No. 16. Hyolithes princeps, Billings. Forma Pingi'eei, Sears. From East Point,
Table showing number of square miles and acres of territory in each
of the seven cities and twenty-eight towns in Essex County, Massachu-
setts, in the year 1903, together with the areas covered by water, swamps,
Cities and Towns in the Codnty
Area in Square
Area in Acres
SURFACE AREAS. (Continued.)
Cities and Towns in the ConNTV
Saugus . . .
Salisbury . .
Swamp scott .
Topsfield . .
Wenham . . .
Nahant . . .
Tidal river valleys and bays
Peat swamps having a depth of 6 to 15 feet . . . .
Fresh-water meadows covered by water in the spring
Parks and roads (in 1898)
Assessable land consisting of village and city sites, uplands, woods,
ELEVATION AND LOCATION OF THE DRUMLINS IN ESSEX
Archelaus hill, West Newbury
Asleb hill, North Andover
Ayer's hill, Haverhill and Methuen . . . .
Bald hill, Boxford
Bald Pate hill, Georgetown
Bare hill, Danvers
Bare hill, Methuen
Bare hUl, Topsfield
Bartholomew's hill, Ipswich
Batt's hill, Salisbury
Beach hill, Salisbury
Bear hill, Merritnac .
Bear hill, North Andover
Berry's hill, Boxford
Blaisdell's hill, Merrimac
Boston hill. North Andover
Brake hill, West Newbury
Brandy Brow hill, Merrimac
Brown's hill, Hamilton
Brown's hill, Ipswich
Brown's hill. South Groveland
Browne's hill, Groveland
Burying Ground hill, Amesbury
Bush hill, Ipswich
Bush hill, Merrimac
Castle hill, Ipswich
Cheney's hill, Groveland
Clay Pits hill. North Andover
Cook's hill, Danvers
Corliss' hill, Haverhill
Crane Neck hill. West Newbury
Crowninshield hill, Topsfield
Cutler's hill, Hamilton
Elliott's hill, Haverhill
ELEVATION AND LOCATION OF THE DRUMLINS IN ESSEX COUNTY (Continued)
Fair Maid's hill, Danvers ....
Farm hill, West Newbtiry ....
Femcroft, or Preston's hill, Danvers
Folly hill, Danvers
Foster's hill. North Andover . . .
Golden hill, Haverhill
Goodale's hill, Peabody
Grape hill, Salisbury and Seabrook
Great hill, Haverhill
Great hill, Topsfield
Hall's hill, Amesbury
Hardy's hill, Groveland
Harris' hill, Methuen
Hathome or Asylum hill, Danvers
Head's hill, Bradford
Heartbreak hill, Ipswich ....
Highlands hill, Merrimac ....
Hill Dale, Haverhill
Holt's hill, Andover
Hopkins' hill, Groveland ....
Howlett's hill, Topsfield
Huckleberry hill, Haverhill. . . .
Hunslow hill, Rowley
Hunting hill, Haverhill
Hutchings' hill, Groveland ....
Ilsley's hill. West Newbury . . .
Indian hill, West Newbury . . .
Jewett's hill, Rowley
Job's hill, Haverhill