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(10). The effects of the static regional metamorphism are
superposed upon the effects of the dynamic metamorphism and
are a consequence of the continuation of anamorphic chemical
changes after mechanical movement had ceased.



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F. H. Lahee — Metamorphism and Oeological Structure. 469

(11). The post-Carboniferous intrusives include a few
minette dikes, on the one hand, and an extensive, perhaps
related, series of granites, pegmatites, and quartz veins (Acid
Intrusive Series), on the other hand.

(12). Of the Acid Intrusive Series, the granite (Boston Neck
granite) is oldest, the pegmatites are younger, and the quartz
veins represent the latest differentiation phase.

(13). The Boston Neck granite is limited to Boston and
Little Necks, the Tower Hill ridge, and westward (Sterling
granite) ; the pegmatites have a wider distribution (within the
Basin), north to Barber's Height and east to Dutch Island ;
and the quartz veins, although most abundant in the south-
western portion of the Basin, occur throughout the area
investigated.

(14). These igneous rocks (Acid Intrusive Series and prob-
ably minettes) were injected during, and immediately sub-
sequent to, the folding of the Carboniferous sediments.

(15). More or less static and dynamic metamorphism attended
the intrusion of these igneous rocks, but this metamorphism is
local and is of a distinctly different character from the regional
metamorphism due to the folding.

We conclude, then, that the Carboniferous strata of the
Narragansett Basin, after deep burial, were folded by forces
that acted with greater intensity in the south ; that, contem-
poraneous with, and consequent upon, this deformation, these
sediments were regionally metamorphosed ; that this deforma-
tion and this metamorphism were accompanied, in their later
stages, by the intrusion of certain igneous rocks — a process
which continued, with magmatic differentiation, for some time
after folding ceased ; and that, these facts being accepted, the
regional metamorphism, and the injection of the post-Carbon-
iferous igneous rocks, may be regarded as nearly parallel effects
of the mountain-building forces.

Cambridge, Mass.,
Febrnaiy 5, 1912.



Am. Joub. Sci.— Foubth Sbbiss, Vol. XXXIII, No. 197.— Mat, 19ia»
81



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^70 e/. E. Eurhank-— One Phase of Microseismic Motion.



Abt. XXXIX. — One Phase of Microseiamw Motion ; by

J. E. BUBBANK.

Seismologists generally include in the term microseismic
motion all pulsations and movements of the earth's crust which
are not attributable to earthquakes or to motion of a more or
less violent and abrupt nature.

Microseisms may be due to local causes, as industrial opera-
tions and ordinary traffic, storms and waves on adjacent shores,
frost action, and possibly by wind, tide, and waves on distant
shores. The kina and number of microseisms recorded at any
place will naturally be limited by the adjustment and damping
of the pendulum and the nature of the record,' as a photo-
graphic registering seismograph with high magnification will
record microseisms when a mechanically registering seismo-
graph would give only a smooth straight line. Moreover, with
mechanical registration the recording surface may not always
be uniformly coated with lampblack and hence will offer vary-
ing resistance to the lateral movement of the writing stylus.
The mechanical registration with low magnification offers a
distinct advantage in studying certain microseisms, since it
does not give such a large mass of detail, hi which it is often
difficult to identify a particular type of motion.

.At the Cheltenham Magnetic Observatory we have been
studying the relation between microseismic motion and the
variations., in atmospheric pressure since 1906, Our seismo-
graph is a two-component, 10 kilogram, horizontal pendulum,
of the Omori type, with mechanical registration and magnifi-
cation of ten times. The periods of the pendulums have been
kept between 24 and 29 seconds. With the seismograph oper-
ating under these conditions, only the more pronounced micro-
seisms are recorded, yet it is " an interesting fact that during
nearly five years record there have been not more than 25 cases
of moderate barometric changes in connection with which mi-
croseisms might have been expected and were not found on
the seismograph traces.

The microseisms accompanying atmospheric pressure vari-
ations have a remarkably regular wave-like motion which almost
always shows a rhythmical increase and decrease of amplitude
indicating interference. The waves occur in groups of from
6 to 12, and vary in amplitude with the intensity of the baro-
metric variation. The most pronounced cases indicate a move-
ment of the earth particles at this place amounting to about
0*05 millimeters on each side of their mean position.
/The resrrlts of our observations from- September 1, 1906, to



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J: E. Burhank-^One Phase of Mioreseimiic M6ti6n. 471

January 31, 1908, were publislied* in tabulftr form, with f nil
notes on the atmospheric pressure conditions. These results
showed that the most pronounced microseisms were almost
invariably connected witn the passage of deep lows across the
coast line from land to sea, or vice versa. It was also pointed
out that the water area under the pressure disturbance would
be in hydrostatic equilibrium, while the land area would be
subject to a stress which would be greatest at the shore line,
.hence we should expect the greatest microseismic motion when
the center of a low area moves rapidly over the coast line.

This reasoning has been confirmed by approximately 100
well-defined cases during the past 5 years; In fact, during the
period under investigation there has not been a single case of a
well-defined low area which has crossed the coast line between
Maine and Florida which has not been accompanied by well-
defined microseisms. It was . also noted in the above paper
that a rapid rising or falling pressure over the coast was
accompanied by microseisms.

This type of microseisms has been studied by Dr. Ott6
£lotz of Ottawa, Canada, who finds that the most marked
cases at Ottawa are connected with the passage of low areas
down the St. Lawrence and into thp Gulf. He considers the
•microseisms due to difference in pressure, which is in agree-
ment with our conclusions.

The movement of a low area down the St. Lawrence and
into the Gulf should be regarded as a passage across the coast
line, although Dr. Klotz makes the statementf that such pas-
sage is not marked by microseisms. This statement is not in
agreement with our results at Cheltenham, which is peculiarly
well located geographically for the study of such phenomena.
Of 300 microseisms recorded here between Septemoer 1, 1906,
and June 30, 1911, all but 32, about 10 per cent, have been
definitely connected with some change of pressure occurring
over the coast line between Labrador and Texas.

That a change of pressure over land areas alone, although of
considerable intensity, does not produce appreciable tremors is
borne out by the following observations ; in many cases intense
depressions have developed over the Mississippi valley Bud
over the Lakes and have moved northward and eastward en-
tirely unaccompanied by microseisms until they had approached
sufficiently near the ocean to cause a steep pressure gradient
over the coast. Another small group iji which a low develops
over the Gulf or the lower Mississippi valley and moves rapidly
northeastward, passing out to sea over the middle Atlantic

♦ Jonrnal Terrestiiftl Magnetism, vol. xiii. pp. 1-20, March, 1908.
f Department of the Interior, Canada, Beport of Chief Astronomer, 1908,
pp. 24-40,



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472 J. E. Burbank — One Phase cf Microeeumic Motion.

states, — in such cases no appreciable microseisms oocnr nntil it
approaches the coast, when they begin and reach their greatest
intensity while the center is passing out to sea. Another very
rare condition is when a low develops over the Gulf states and
moves northeastward along the AIK^heny mountains, oassing
into Canada without producing any great pressure cnanges
along the coast line ; in such cases no microseisms are recogni-
zable. Still another very rare case is when a low develops
over the ocean east of Florida and recurves northwestward,
passing inland over the South Atlantic coast. The micro-
seisms rapidly decrease after the center passes inland, although
it may still l>e of considerable intensity.

Of the 268 microseisms recorded here during the last 5 years
and which appear connected with atmospheric variations,
approximately two-thirds occur in tlie period October to April,
when pressure changes are more frequent and abrupt ; they
occur very rarely during June, July, and Angust, when pres-
sure gradients are very small. Dnring these winter months
these microseisms often continue for several days, diminishing
and increasing in intensity as a succession of abmpt pressure
changes from low to high sweep over the coast into the Atlan-
tic Ocean.

A detailed study of all these cases confirms the general con-
clusions already set forth in connection with my earlier paper ;
hence the tabulation and detailed notes are omitted from this
paper, and only conclusions stated.

Of the 268 microseisms above mentioned, 74 were connected
with lows moving over the Gulf of St. Lawrenpe ; 20 of these
were of sufficient amplitude to determine the period, which
varied from 2*8 to 3-5 seconds, with 4 cases of 3*6, 4-6, 5-0,
and 6 seconds respectively — 68 lows moved wholly or in part
over the coast of if ew England ; of these 21 sliowed periods
ranging from 3*0 to 3*5 seconds, with one 3*8, one 4*0, and two
5'0 seconds, the remainder being too ill-defined to allow deter-
mination of period — 73 microseisms were connected with pres-
sure changes occurring over the Middle Atlantic coast between
New York City and Cape Hatteras ; nearly all of these were
lows and show periods ranging from 3*0 to 3'5 seconds, with 6
cases ranging from 3*8 to 5*0 seconds. There were 20 cases
connected with the South Atlantic coast, nearly all being due
to lows passing northeastward into the ocean and often moving
northward parallel to the coast with decreasing intensity ; most
of these gave intense microseisms with the usual period, one
case having a period of 50 seconds ; in addition to these
were 13 cases of lows forming in the Gulf, or the ocean east
of Florida, also including hurricanes which approach the Flor-
ida peninsula or the Gulf coast ; these show the usual periods



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J. E. Burhaiik — One Phase of Mioroseismio Motion. 473

with one marked exception : on October 16-17 a hurricane,
with pressure about 29*05 inches, was in the Gulf southwest
of Florida and the microseisms had a period from 6*0 to 6'8
seconds; on the 18th, when the center had approached the
Florida coast and was passing inland, the period had decreased
to 3'5 seconds and the amplitude ^^reatly increased.

In general the period of the microseisms is from 3*0 to 3*5
seconds regardless of the part of the coast under strain. Peri-
ods greater than 3*6 seconds apparently occur only when the
low IS of great extent and the center almost wholly over the
ocean. It would appear from this that the period of the micro-
seisms varies with the extent of the disturbed water area.

In general, pressure changes due to high areas are too grad-
ual and widespread to produce microseisms of appreciable
intensity, although about 40 cases have been noted, nearly all
being cases in which a depression was closely followed by a high
area of marked intensity.

In my earlier paper it was su^ested that the microseisms
might be connected with the movements of large masses of
water set in motion by the wind accompanying the pressure
changes. This assumption is not borne out by a comparison
of the winds, normal to the coast line, and the microseisms
occurring during the period January 1 to June 30, 1910.
During this period there were strong microseisms on days when
there was little or no wind along the coast, and also days when
there were high winds without any well-marked microseisms.
In general, high areas are accompanied by winds when they
approach the coast, although they are rarely accompanied by
microseisms.

Another point of interest is that the period of the micro-
seisms does not appear to be conditioned by the geological nature
of the part of the coast line over which the low is passing, as
all parts of the coast give essentially the same periods. It
seems probable that this period is a characteristic of the local-
ity in which the seismograph is mounted, although the change
of period during different microseisms is ditBcult to explain on
that basis. Klotz at Ottawa observed periods of 5 to 6 seconds
with occasional changes to 3 seconds.

The above conclusions by no means preclude the probability
of microseisms being produced by the movement of lows and
highs wholly over Sie land area ; in fact it is extremely prob-
able that they do occur, and could be readily recorded by a
sufficiently sensitive seismograph, but it is evident that, at least
for the eastern part of the United States, the most marked
microseisms are those related to the variations of pressure
along the coast line.



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474 J. E. Bwrbank — Microseisms Caused hy Fro9t Action.
Art. XL. — Microsei^ms Caused hy Frost Action ; by J. E.

BiTBBANK.

In a paper on " Some Apparent Variations of the Vertical
etc."''^ the writer called attention to a class of minnte earth
movements or microseisms of very small amplitude and irreg<
ular period varying from 8 seconds to 2 minutes. At that
time only a few cases had been identified.

Kecently an abstract of a paper by B. Gutenbergf has come
to my attention. In this abstract it is stated that the distri-
bution of frost in southwestern Europe up to about 60*^ N.
Lat. and 30** E. Long, can be determined from the records of
the 100 kilogram pendulum of the Geophysical Institute at
Gottingen. The movement showed a well-defined daily period,
max. about 6 a. m. and min. about 3 p. m. and an amplitude
which on one occasion showed an earth movement in the
north-south direction as great as ^ millimeter on each side of
the position of rest. One would infer that these microseisms
sometimes occur when the ground at some distance is freezing
and thawing, while at Gottingen it was not frozen. It is diffi-
cult to understand how the expansion and contraction of the
surface layers in freezing and tnawing can produce vibrations
or variations of level of sufficient magnitude to be recorded
more than a few kilometers beyond the frost zone.

Cheltenham is so located that the approach of cold waves
and freezing of the ground can be studied several days before
they reach us, and often the zone of frost is only a short
distance, 100 to 200 kilometers, to the north of the station,
while the ground at Cheltenham is not frozen. Our pendulums:^
are not as sensitive as those used by Gutenberg, and a move-
ment of the earth particles of less than -02 millimeter would
not be recognized.

An examination of our seismograms for a period of several
years past shows that whenever actual freezing or thawing of
the ground is taking place at Cheltenham these microseisms
are recorded as irregular tilts or movements of the pendulum
back and forth in a somewhat jerky and irregular manner.
The most common period is between 8 and 14 seconds, but
they frequently have a period as great as two minutes. The
amplitude increases with the intensity of the freezing or thaw-
ing, the usual range of motion of the earth particles being
between "02 and '10 millimeters. These microseisms are con-

* This Jonmal, vol. xxx, Nov. 1910, p. 832.
t JE^hysikalUche Zeitschrift, 191T), pp. 1184-5.
X See preceding paper.



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J. E. Burbanh^MioroseUms Caused by Frost Action. 475

tinnouB as long as the ground is frozen and continue without
appreciable diminntion when the frozen ground is covered
with a blanket of snow. When the ground is covered with
snow the microseisms are due to the thawing out of the lower
layers of frozen ground in contact with the warmer layers
below.

Attention was especially directed to those cases of cold
waves with freezing temperatures approaching Cheltenham
and in no case could any microseisms be detected until the
ground at Cheltenham had begun to freeze.

The above evidence does not disprove a relation between
niicroseisms and frost action at a distance, but it places a limit
on the magnitude of such action.

Cheltenham, Md., Angust, 1911.



Art. XLI. — DahUite (Podolite) from Tonopah^ * Nevada;
Vodckeritej a New Ba^ic Calcium Phosphate; Eem^rks
on the Chemical Composition of Apatite and Phosphate
Hock ; by Austin F. Eogbrs ; witn Analyses by 6. E.

POSTMA.

My attention was directed to a chemical study of apatite
and related minerals by the recognition of a calcium caroono-
phosphate on a mineral specimen from Tonojjah, Nevada,
kindly sent to me by Mr. S. C. Herold, a mining engineer.
This specimen, which is from the Mizpah mine of the Tonopah
Mining Company, consists of iodyrite, hyalite, quartz, man-
ganese dioxide, and a white drusy coating of minute hexagonal
crystals. As these hexagonal crystals seemed to eflEervesce in
acid, they were provisionally referred to calcite. Optical tests
failed to confirm this determination, for the fragments had
weak, instead of strong, double refraction. The weak double
refraction suggested apatite. As a good phosphate test was
obtained, the mineral naturally was called apatite and the effer-
vescence was attributed to an error in observation.

On reading a paper* on the probable identity of dahllite with
podolite, it occurred to me that the Tonopah mineral might
belong to one of these carbono-phosphates, so the solubility
test was tried again very carefully. There was distinct effer-
vescence with warm nitric acid. Observed under the micro-
scope, the bubbles come from the hexagonal crystals and from
♦ Schaller, this Journal, vol. xxx, 809, 1910.



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476 Rogers — DahlUte ( Poddite) from Tonopah^ Nevada.

irregular fragments with weak double refraction, so the effer-
vescence is not due to admixed calcite. Moreover, there is
practically no effervescence until the acid is heated. Good
tests for calcium and the phosphate radical and a slight test
for chlorine were obtained. A faint test for fluorine was
obtained by heating the powdered mineral with silica and con-
centrated sulphuric acid, and condensing the fumes on moist-
ened black paper.*

To further prove the identity of the mineral, chemical
analyses were made by Mr. G. E. JPostma, chemistry student at
Stanford University. Unfortunately, a very limited amount
of material was available. The carbonate and phosphate
radicals were determined in a large, very impure sample with
these resultsf (average of two) :

CO, 1-56

PO, 29-64

In a much purer sample consisting of only 74 mg., calcium,
fluorine, and the phosphate radical together with insoluble
matter (principally quartz) were determined with the following
results :

Ca 32-56

PO, 47-03

F 0-29

Insol 12-72

The amount of carbonate radical in the sample can be cal-
culated from the preceding analysis. The excess of oxygen
can be obtained by subtracting the amounts of the constituents
in the form given above from the amounts in the ordinary form
of oxides. This oxyeen excess amounts to 1'07 per cent. "We
then have the f oUowmg figures :

Molecular ratios

Ca 32-56 0-814 10-00

PO^ 47-03 0-495 6-08

F, 0-29 0007)

(CO, 2-48) 0-041 VO-IU 1-40

(O 107) 0-066)

The fluorine percentage is probably low, as it usually is.
The ratio of Ca, rO„ (CO,, F„ O) is very closely 10:6:1, slight
errors probably giving high oxygen. The Tonopah mineral
can be interpreted as an isomorphous mixture of 3Ca,(P0^),.
CaCO,, 3Ca.(PO,),.CaO, and 3Ca.(P0j..CaF,. It is necessary

* Browning, this Joamal, vol. xxxii, 249, 1911.

f In accordance with the modem yiews of chemistry, analyses are recorded
in the form of metals and acid radicals.



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Rogers — Dahllite ( Podolite) from Tonopah^ Nevada. 477

to assntne that oxygen i^eplaces fluorine and the carbonate
radical on aeeouDt of tlie small amounts of these constituents.
As the carbonate-phosphate molecule is present to the extent
of at least half, the mineral should be called dahllite (or
podolite).

The optical properties of the mineral are also interesting.
The crystals are hexagonal tabular in habit as repi*esented in
figure 1. The interior of the crystals is almost opaque white,
wnile the exterior is subtransparent. The central portion of

Fio. 1.





DahUite (Podolite) from Tonopah, Nevada.

the crystals, including a narrow zone of the subtransparent
part (black area of fig. 2), is dark between crossed nicols, while
the remainder of the subtransparent exterior is double refract-
ing and divided into six sectors. These sectors extinguish in
opposite pairs at an angle of 7*^ or 8*^ with the edge as
indicated in fig. 2 and give negative biaxial interference figures
in convergent light.

The hexagonal prism is either |6170( (or {1670}) with axial
plane parallel to |10lO[ or it is jlOlO} with axial plane
parallel to }6170i (or 11670}), for the theoretical angle
(lOlO A 6170) is T 35'. If the prism is 1 6170}, as seems prob-
able, the crystals have the symmetry of the hexagonal
pyramidal or apatite class.

In the podolite described by Tschirwinsky* the biaxial sec-
tors extend to the center of the crystal. The question arises
as to whether all the Tonopah mineral, or only the exterior, is
dahllite (podolite). This can not be definitely settled as the
mineral contains some fluorine and also an excess of oxygen,
but probably the exterior of the crystals more nearly approaches
dahllite (podolite) than the interior.

The formula for podolite established by Tschirwinskyf is
3Ca,(P0^)a.CaC0,. Schaller:]: gives good arguments for con-
sidering podolite and dahllite as identical. The name dahllite
given by Brdgger and Biickstrom§ has priority.

* Centralblat. Mineral., etc., 1907, pp. 279-283. f Loc. eit.

X Loc. cit.

§ Ofy. Akad. Stockh., zlv, 498, 1888 ; Dana System, 6th ed., p. 866.



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478 Eager 8 — DahUite ( Podolite) from Tonopnh^ Nevada.

The isotnorphism, or at least the replacement of fluorine bj
the carbonate radical, is proved by several analyses* of apatite
taken from the literature.





Ca


PO4


F


CO.


CI


Portland, Canada

Londongrove, Penn

Templeton, Canada . . . .


38-62
38-53

37-77


54-03
55*40
55-52


338
1-95
1-17


1-17
1-93
3-14


0-09
0-94
0-42



The second analysis, made by Carnot,t corresponds almost
exactly to the formula 3Ca,(P0,),.Ca(F„Cl„C0,).

I have examined apatite from fourteen different localities
and have found that, with one possible exception, they give
effervescence in hot nitric acid. These incluae apatites from
Canada, Arkansas, ^Norway, among them both nuor-ai)atites
and chlor-apatites. It may seem strange that fluorine and the
cai*bonate radical should replace each other and that the com-
pounds 3Ca,(P0,)..CaF, and 3Ca,(P0J,.CaC0. should be
isomorphous. The isomorphism of these compounds can be
explained by the mass-effect of 3Ca,(P0J,.Ca (formula weiffht
=971) in these compounds ; the fluorine and carbonate radical
have relatively little influence. This explanation of isomor-
phism we owe to Peufield, who explained the chemical com-
position of tourmaline by the mass-effect of Al,(B.0H),8i^0i,
m the molecule H,Al,(B.OH),Si^Oj„ it making little difference
whether the hydrogen is replaced bj^ aluminium, magnesium,
iron, or the alkalies. The isomorphism of PbFe/OHjijXSO^X
(plumbojarosite) with K,Fe.(OH),,(SO,\ (jarosite) Penfield
explained in the same way. A similar explanation will doubt-
less hold for other mineral groups.

A critical study of apatite analyses will convince one of the
existence of a basic calcium phosphate, for many of the
analyses show a deficiency of both fluorine and chlorine and
also of the carbonate radical. In tabular form I have collected.'
here several apatite analyses showing this deficiency. The
oxygen is obtained by subtracting the sum of the constituents
in tne present form from their sum as oxides. The almost
perfect summations prove that this is justified. It was thought



Online LibraryJohn Elihu HallThe American journal of science → online text (page 47 of 61)