Rodolfo Amedeo Lanciani.

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* OoDtact seemed to be established simultaneously at several points,
f Doubtftil Limbs " certainly in contact by at least that time.**
Ax. JouB. Soi.— Sbookd Sbribs, Vol. L, Pio, 148.— Jult, 1870L
6



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82 & Newcomb on observing the eommg Ihmaita of Venus.

ments employed in observing the transit of Venus, in order to
determine what correction should be applied to the observa-
tions of one to make them comparable witn those of the other.
It would be a comparatively simple operation to erect an artifi-
cial representation of the sun's disk at the distance of a few hun-
dred yards, and to have an artificial planet moved over it by
clockwork. The actual time of contact could be determined by
electricity, and the relative positions of the planet and the disK
by actual measurement* With this apparatus it would be easy
to determine the personal errors to which each obflerver was lia-
ble, and these errors would approximately represent those of the
observations of actual transit

Still, it would be very unsafe to trust entirely to any deter-
mination of ingress or egress. Understanding the uncertainty
of such determinations, the Gterman astronomers have proposed
to trust to measures with a heliometer, made while the planet
is crossing the disk. The use of a sufficient number of heUom-
eters womd be both difficult and expensive, and I think we
have an entirely satis£su:tory substitute in photography. In-
deed, Mr. De la Rue has proposed to determine the moment
of internal contact by photography. But the result would be
subject to the same uncertainty which affects optical observa-
tions — ^the photograph which furst shows contact will not be that
taken when the thread of light between Venus and the sun's disk
was first ccHnpleted, but the first taken after it became thick
enough to affect the plate, and this thickness is more variable
and uncertain than the thickness necessary to affect the eya
We know very weU that a haziness of the sky which very
slightly diminishes the apparent brilliancy of the sun, will very
materially cut off the actmic rays, and we photographic plate
has not the power of adjustment which the eye has.

But, although we cannot determine contacts by photography,
I concdve that we may thereby be able to measure the mstance
of the centers of Venus and the sun with great accuracy. Hav-
ing a photograph of the sun with Venus on its disk, we can,
with a suitable micrometer, fix the position of the center of each
body with great precision. Wecanthen measure tiie distance of
the centers in inches with corresponding precision. All we then
want is the value in arc of an mch on the photograph plate.
This determination is not without difficulty. It wiU not do to
trust the measured diameters of the images of tiie sun, because
they are affected by irradiation, just as the optical image is. If
the plates were nearlvof the same size, and the ratio of we diam-
eters of Venus and tne sun the same in both plates, it would be
safe to assume that they were equally affected by irradiation.
But should any difference show itself it would not be safe to as-
sume that the light of the sun encroached equally npon the dark



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T. & HutU on the Geology of Eastern New MiglancL 8S

ground of Venus and upon the sky, because it is so much fidnter
near the border.

If the photographic telescope were furnished with clock-work,
it would be advisaole to take several photographs of the Pleiades,
both before and after the transit, to mmish an accurate standard
of comparison jfree firom the danger of systematic error. There
is little doubt that if the telescopes and operators practiee
together, either before or after the transit, dfitta may be obtained
for a satis&ctory solution of the problem in question^

To attain the object of the present paper, it is not necessity
to enter into details respecting choice oi stations and plans of
observation. I have endeavored to show that no valuable re-
sult is to be expected from hastily-organized and hurriedly-
ejjuipped ^peditions ; that every step in planning the observa-
tions require carefdl consideration, and that in ail the prepara-
tory arrangements we should make haste very slowlv. I make
this presentation with the hope that the Academy will take such
action in the matter as may seem proper and desirable.



Abt. XL — On the Geology of Eastern New England; by Dr.
T. Stebrt Hunt, F.R& (From a letter to Pro£ tJAHBS
D. Dana.

Whsn, more than twenty years since, my attention was
turned to the geology of New England, there was no evidence
of the existence between the old gneisses of the Adirondacks
and the coal measures, of any other stratified rocks than those
of the Huronian seri^ and the New York system, from the
Potsdam formation, upward. It is true that Emmons had«
before that time, maintained the presence, in western Vermont
and Massachusetts, of a svstem oi fossiliferous sediments, lying
unconfoimably beneath tne Potsdam, but the evidence up to
this time adduced with regard to these so-called Taccmic rocks,
has failed to show that tney include any strata more ancient
than the Potsdam, while most of them are certainly younger.
The researches of Sir William Logan, up to 1848, had led him
to refer to a period not older than the Lower Silurian the crys-
talline sediments of the Appalachian rcmon of Canada, between
Lake Champlain and Quebec. These K^rm a chain of hills, th^
continuation of the Green Mountains, and were found by him to
be followed immediately, to the southeast, by more or less calca-
reous and somewhat altered strata, associated with Upper Silu*
rian fossils, and succeeded, across the strike, near the sources of
the Connecticut Biver, by a series, several miles in breadth, of
micaceous schists and quartzose strata, occasionally containing



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84 T. S, Hunt an the Geology of Eastern New England.

chiafltolite, garnet and homblenda These two series of rocks,
extending from the base of the Green Mountains to Canaan
on the Connecticut, it was suggested by Sir William Logan, in
his Report on the Geological Survey, 1847-1848, might oe the
altered representatives of the rocfa of Qtwp^, including the
Lower Helderberg groijp, and the succeeding members of the
New York system to the top of the Chemung. I then, as now,
conceived- that these micaceous and argillaceous schists, often
holding garnets and chiastolite, were identical with those which
make so conspicuous a figure in the White Mountains, and else-
where in Eastern New England, and when, in 1849, I laid
before the American Association at Cambridge, the results of
the Geological Survey of Canada (this Jour., EC, ix, 19), sug-
gested that to the Gtisp^ series, as above defined, '^ may perhaps
be referred, in part, the rocks of the White Mountains. Les-^
ley, subsequently, in 1860 (Proc. Philad. Acad. Nat Sciences,
page 363), adduced many reasons for believing that the rocks of
these mountains might be strata of Devonian aga* Li the large
geological map of Canada and the northern United States, lately
published by Sir WUliam Logan^ no attempt \a made to deline-
ate the geology of New Hampshire, but the rocks in question,
to the north of the United States boundary, are represented as
Upper Silurian, with the exception of a belt of the Quebec
group, which has been recognized in that region.

Li facl^ the schists and gneisses of the White Mountains are
clearljr distinct, lithologically, fix)m the Laurentian, the Lab-
radonan and the Huronian,' as well as from the crystalline
rocks of the Green Mountains, and from the fossiliferous Upper
Silurian strata which lie at the southwestern base of the (Cana-
dian prolongation of the latter. Having thus exhausted the
list oi known sedimentary groups up to tms horizon, it was evi-
dent that the crystalline strata of the White Mountains must
be either (1) of Devonian age, or (2) something newer (which
was highly improbable) ; or (8) must belong to a lower and hith-
erto unknown series. In the absence of any proof^ at that
time, of t^e existence of such a lower system, the first view,
which referred these strata to the Devonian period, was the only
erne admissible.

* In this ooDneotion should be recaJled the views put forth m 1846, by MeBsra.
H. D. and W. B. Bogera, in ft paper on the Geolpgioal Age of the White Mountains,
(this Journal, n, i, 411). Thej there, for the first time, pointed out that the great
mass of these mountains consists of more or less altered sedimentary strata^ which,
upon the evidence of supposed organic remains, they referred. wiUi some little
doubt, to Ihe Clinton division of the Upper Silurian. In 1847, however, they an-
nounced that &e supposed fossils, on whidi this identification had been founded,
were not really such, (this Journal, n, v, 116). Future explorers may, it is hoped,
be more sucoessftil, and yet discover among the strata of the White Mountains
evidences of organic life, probably of primoidial Silurian age.



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T. & Hunt on the Geology of Eastern New JEnglond. 85

When, however, ftirther investigation showed that the great
and progressive thickening which takes place in the paleozoic
formations fix>m the west, eastward, is not confined to the aug-
mentations of existing subdivisions, but includes the intercala-
tion of new ones ; when the few hundred feet of typical Pots-
dam sandstone in New York are represented in Vermont,
Quebec and Newfoundland, by thousands of feet of strata
lithologically very unlike the type ; while the Quebec group,
not less in volume, appears representing the beds of passage
between the Calciferous and Chazy divisions of New York, we
begin to conceive that conditions of sedimentation, very unlike
anything hitherto suspected in the west, prevailed to the east-
ward. When, moreover, we find widely separated areas of
Labradorian and Huronian rocks, — remaining fragments of great
series, — ^resting upon the Laurentian, from Lake Huron to New-
foundland, we get evidences of a process of denudation in past
ages, not less remarkable than the sedimentation.

My observations of last year have led me to a conclusion,
whicn had previously been taking shape in my mind, that there
exists above the Laurentian, a great series of crystalline schists,
including mica-slates, staurolite and chiastohte-schists, with
quartzose and homblendic rocks, and some limestones, the
whole associated with great masses of fine-grained gneisses, the
so-called granites of many parts of New England The first
suggestions of this were given me by the observation of Dr.
Bigsby, confirmed by specmiens since received from the region,
that there exists to the northwest of Lake Superior, an extended
series of crystalline schists, unlike the Laurentian, and resem-
bling those of the White Mountains. I have already called
attention to this resemblance in, a review of the progress of
American Geology, in 1861 (this Jour., II, xxxi, 895). It was
contrary to my notions of the geological historv of the continent
to suppose that rocks of Devonian age could, in that region,
have assumed such lithological characters, and I was therefore
led to compare these rocks with a great series of crystalline
schists, abounding in mica-slates and micaceous limestones,
which occupy considerable areas in the Laurentian region in
Hastings county, to the north of Lake Ontario. The distribu-
tion 01 this series has been traced out by Mr. Vennor, who, in
1869, was able to show that, although much contorted, it rests
unconformably upon the old Laurentian gneisses, while it is, at
the same time, overlaid by the horizontal limestones of the
Trenton group. This intermediate series, which attains a thick-
ness of several thousand feet, is terminated by calcareo-mica-
ceous schists, in which Uozoon Ganadense has been found, both
in Madoc and in Tudor. In these localities, as shown by Daw-
son and Carpenter (this Jour., II, xliv, 867), the calcareous



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86 T. S. Sunt on the Geology of Eastern New England.

skeleton of the Eozoon, instead of being injected by serpentine
or another sUicate, is simply filled with impure calcareous and
carbonaceous matter. The presence of this fossil serves to con-
nect these rocks with the Laurentian ^t^n, with which they
had provisionally been classed, although their lithological dis-
similarity had long been noticed, and in 1866 Sir William
Logan had remarked their resemblance to the mica-slate series
found near the sources of the Connecticut River (Report Geol
Survey, 1866, p. 98).

Mr. Alex. Murray's report of his explorations in Newfound-
land, published in 1866, throws much light on the history of
the rocks immediately succeeding the Laurentian in that r^on.
He found in the great northern peninsula, about the Cloud
Mountains and Canada Bay, not less than 5400 feet of strata,
referred by him to the Potsdam group. Of these the lower 2500
feet consist of bluish-gray slates, holding near the summit, beds
which become conglomerate fi^om the presence of quartz peb-
bles, and are followed by a mass of purplish amygdaloidal dio-
rite, holding epidote and jaspery red iron ore. Then follow
2000 feet of argillaceous and somewhat micaceous slates, with
beds of quartzite and of limestone, generally impure. These
contain, oesides numerous fucoidal markings, the remains of a
Lingula, and of Olendhis Vermontanus, a fossil characteristic of
the rotsdam group. To this second division succeeds a third,
consisting of about 900 feet additional of limestones and slates.
Somewhat farther southward, at Great and Little Coney Arms,
the lower half of the above series is not observed, but a succes-
sion of strata, supposed to represent the upper portion of the
Potsdam, is more particularly described. It consists, at the base,
of 800 feet of pale bluish-gray mica-slates, with iron staios,
"softer, more finely laminated, and more uniform both in color
and in texture " than some micaceous strata described by Mr.
Murray as occurring in the Laurentian in that region. To these
succeeded 480 feet of similar soft bluish-gray mica-slates, holdinc
numerous thin seams of dark colored limestone, and followea
by 1000 feet of impure limestones and slates, often micaceous
and calcareous, among which are a few beds of white compact
marble. No indications of fossils, save fucoidal markings, were
met with in this section. At Coney- Arm Head there is seen a
series of " whitish granitoid, very quartzose mica-slates," which
appear to have a thickness of n-om 1500 to 2000 feet The
same rock is found in White Bay, where it overlies what is sup-
posed to be Laurentian gneiss. The relations of these whitish
^anitic mica-slates are still obscure, but Mr. Murray was
inclined to regard them as occupying a position beneath the
Potsdam group. The latter, in Canada Bay, is immediately
followed by the unaltered fossiliferous limestones and shales of



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T. & Hunt on the Geology of Eastern New England. 87

the Quebec group. From these investigations of Mr. Murray
we learn that between the Laurei^tian and the Quebec group,
there exists a series of several thousand feet of strata, including
soft bluish-OTey mica-slates and micaceous limestones, belong-
ing to the rotsdam group ; besides a great mass of whitisn
granitoid mica-slates, whose relation to the Potsdam is still
uncertain. To the whole of these we may perhaps give the pro-
visional name of the Terranovan series, m allusion to the name
Newfoundland.

Imperfect gneisses and micaceous schists are found in several
parts of the province of New Brunswick, associated with what
has been described as a great granitic belt These rocks have
been examined by Prof Hind, and by Mr. Robb, on the St
John and Mirimichi rivers ; and the former of these observers
some years since pointed out the indigenous character of the
so-called granitea In the summer of 1869 1 had an opportunity
of examining, with Prof L. W. Bailev, the region about St
Stephen, on the river St Croix, where he had already observed
a series of ferruginous quartzites and imperfect ffneisses, accom-
panied by soft bluish mica-slates sometimes holding chiastolite,
staurolite, and garnet These highly crystalline schists are not
more than five miles removed fix)m imaltered shales of the
Gasp6 series, containing fossils of Upper Silurian or Lower
Devonian Wpes, and rest unconformably upon older granitoid
rocks, which rrof Bailey regards as probably Laurentian. We
subsequently examined the crystallme schists of the St John,
which are apparently identical with those of the St Croix, and
these also overlie, unconformably, an older granitoid gneisa

More recently Prof Hind has pointed out that some of the
so-called granites of Nova Scotia are ancient gneisses, probably
of Laurentian age, and have shown that between these and the
gold-bearing slates of that province, there is found, near Wind-
sor, and near Sherbrooke, a series of beds of no great thickness,
consistinff of imperfect gneisses, quartzites and micaceous
schists, which rest unconformably on the Laurentian, and are
sometimes wanting altogether. These include mica-schists with
chiastolite and garnet, and appear identical with those alreadv
observed by Dr. Dawson in other parts of Nova Scotia, which
I had already recognized as the same with those of the White
Mountains, and those of the St Croix, just noticed. Prof
Hind, in a late paper, has called these, from their position in
Nova Scotia, Huronian ; but the Cambrian or Huronian rocks
recognized by Messrs. Matthew and Bailey in New Brunswick,
where they are widely spread along the north side of the Bay
of Fundy, consist of massive diorites and quartzose feldspar-
porphyries, with occasional sandstones and conglomerates, and
are very unlike the gneissic and micaceous rocks in question,



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88 T. & Hunt on the Geology of Eastern New England.

which I believe to belong, like those of the St Croix and
the St John rivers, to the great Terranovan series. The mica-
ceous and homblendic sclusts, with interstratified fine grained
whitish gneisses (locally known as granites^ which I have seen
in Hallowell, Augusta, Brunswick and Westbrook, in Maine,
appear to belong to the same series ; which will also probably
include much of the gneiss and mica-schist of Eastern New
England. If this upper series is to be identified with the crys-
tallme schists whicn, in Hastings County, Ontario, overue,
unconformably, the Laurentian, and yet contain Eozoon Cana-
denssj the presence of this fossil can no longer serve to identify
the Laurentian system. To this lower horizon however, I have
referred a belt oi gneissic rocks in Eastern Massachusetts, which
are lithologically unlike the present series, and identical with
the Laurentian of New York and Canada. To the upper series
appear to belong the great endogenous granitic veins so well
IcQown to mineralo^sts as containing beryl, tourmaline and other
fine crystallized minerals.

The fine-grained, white granitoid gneisses, often present an
apparently bedded structure, which enables them to be removed
in large plates or layers, lying at no great angle, and appar-
ently conformable to the present surfiice of the coimtry. This
structure, which I conceive to have been superinduced by super-
ficial changes of temperature, is often quite independent of the
bedding, as may be seen in the quarries near lA^ugusta in Maine,
and in the cuttings on the Grand-Trunk Railway near Berlin
Falls, New Hampshire. It is also observed in exotic or intru-
sive granites, like those of Biddeford, Maine. This is, in fact,
the concentric lamination of granite, long since observed by
Von Buch, and, I believe, correctly explained by Prof N. S.
Shaler to be due to movements of contraction and expansion in
the mass, caused by variation of temperature during the changes
of the seasons. He has not however observed this structure at
greater depths than from three to five feet, while in some rocks
I have found it penetrating probably twenty feet (See Shaler's
paper, read before the Boston Nat History Society, Feb. 3,
1869, and published in the Proceedings of the Society, vol. xii,
page 289).

While however I admit the existence in the Dominion of
Canada and in Eastern New England, of a great series of crys-
talline schists, distinct fi:om the Laurentian, and apparently the
same with those found by Mr. Murray between the Laurentian
and the Quebec group in Newfoundland, it is not less certain
that we have in these re^ons rocks of Upper Silurian and
Lower Devonian aee, holding characteristic fossils. These
strata in Maine ana New Brunswick are generally but little
altered. In the Connecticut valley at Bernardston, Massachu-



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T. & Stmt on the Geology of Eastern New Migkmd. 89

setts, near Lake Memphremagog in Vermont, and ftirther north-
ward in the province of Quebec, fossik of this horizon are found
in rocks which, in some localities, are more or less altered and
crystalline. I believe however that much of the calcareous mica-
slate of Eastern Vermont will be found to belong to the Terra-
novan series. The extent of these newer rocks, and the limits
between them and the more ancient schists, of the ruins of which
they are probably in part composed, remain problems for farther
investigation. For tne solution of these. Prof. C. H. Hitchcock,
by his labors in Vermont, is already well prepared, and it cannot
be doubted that he, with his able assistants, will in the Survey
of New Hampshire, now in progress, throw much light on New
England geology. It is worthy of remark, that strata holding
fossils of Lower Helderberg a^e, or thereabouts, are not confined
to the shores of Maine ana New Brunswick, and the valleys of
the Connecticut and St John rivers, but are found beyond the
Green Mountains, in the vallev of the St Lawrence, near Mon-
treal ; where, on the island of St Helen, they rest unconform-
ably on the Utica slate, and at Beloeil Mountain, near by, on
intrusive diorites, which there break through the shales of the
Hudson River group.

The relations of this Terranovan series to the porphyries and
diorite rocks which, in New Brunswick, have b^n caUed Cam- •
brian and Huronian by Mr. Matthew (first distinguished by
him as the Coldbrook group), yet remams to be determinei
These rocks are found near to the city of St John resting
directly on what has been regarded as Laurentian, and are over-
laid by the uncrystalline schists which contain the primordial
fauna now so well known by the descriptions of Prof Hartt
Rocks which I regard as identical with this same Coldbrook or
Cambrian group, are found along the coast of New Brunswick,
and constitute the diorites and porphyries of Eastport, Maina
They appear moreover to be the same with those met with near
Newburyport, and at Salem, Lynn, and Marblehead, Massachu-
setts, i'arther researches about Passamaquoddy Bay, where
the mica-slates are found not far removed from these porphyries,
will probably enable us to determine their relations to each
other.

It will be remembered that Gtimbel has found, in Bavaria,
beneath the oldest fossiliferous clay-slates, a mica-schist (and horn-
blende-schist) series, reposing upon the Hercynian gneiss, which
contains crystaUine limestones, with grapmte, serpentine and
Eozoon Oanadense^ and which he has identified with the Lauren-
tian of North America. He distinguishes beneath this a great
mass of red gneiss, apparently without limestones, to which he
has given the name of the Bojian gneisa It will however be
remembered, that in his studies of the Laurentian system on the



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90 (X U, JShqpard, Sr. — Minerahgical OontribtUions.

Ottawa, Sir William Logan has shown that this immense series
(his Lower Laurentian), some 20,000 feet in thickness, includes
four great masses of gneiss and quartzite, divided by three lime-
stone formations, and that it is in the uppermost of these, which
is, in some parts, 1500 feet thick, that tne Bozoon Oanadense has
been found. Some of the lower gneisses of this vast system
may very well represent the Bojian of Gumbel, who has not
recognized in Bavaria either the Labradorian (Upper Lauren-
tian) or Huronian series. (See Gumbel on the Laurentian of
Bavaria, translated and published in the Canadian Naturalist
for December, 1866). Comparative studies of this kind should
not be neglected in the investigation of our American rocka
Montreal, May 10, 1870.



Aet. Xn. — Mineralogiml Contributions; by CHARLES Upham



Online LibraryRodolfo Amedeo LancianiThe American journal of science and arts → online text (page 62 of 109)