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actually exists in solid solution, this at present must be regarded
as pure conjecture. The albite molecule, if present, would
have very peculiar properties, entirely unlike albite as it exists
either in pure condition or isomorphous with other feldspars,
since nephelite with its excess of silica is completely soluble
in N/4 hydrochloric acid. This evidence, however, we recog-
nize fully is not proof that the albite molecule is absent. It
cannot be proved either way at present. Hence our point,
that it is better to leave the question as to the molecular con-
dition of excess of silica entirely open.

There is one point regarding the amount of silica which
nephelite can take up, which needs mention. Bowen states
(p. 53) : " It is therefore only in the presence of albite itself
that nephelites may be expected to be saturated with silica."
This is a conclusion which we also drew in our article, but later
Bowen states : " The conditions necessary for the saturation of
nephelite with albite are so unlikely to occur that it may
be safely said that natural nephelites are probably never
saturated." It was shown in our former article that three
nephelites, which were associated with albite, and one asso-
ciated with microcline-microperthite, exhibited a constant
maximum ratio for silica, and we suggested that this repre-
sented the saturation value. The objection could, perhaps, be
raised that the nephelite and albite were not formed simulta-
neously, so that the former was not necessarily saturated.
Probably no one will doubt the assertion that if a magma
deposits both nephelite and albite together, the former must
be saturated witn silica at the temperature of solidification.
There is plenty of evidence that this process has taken place.

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Foots and Bradley — Chemical CompoBitimi of Nephelite. 441

It has been shown by Bayley* and by Morozewiczf that rocks
occur where both nephelite and very pure albite must have been
formed simultaneously. Morozewicz in particular has shown
that in the rock investigated by him, albite crystallized
throughout the entire time when nephelite was forming. The
nephelite in both rocks was analyzed. It is probable that the
material was not as carefully purified as in the cases considered
in our former article, since the object was to show that neph-
elite was present and not to derive its formula. Still, the
results should show approximately the limiting ratio for silica,
when nephelite is saturated. The ratios calculated from their
analyses are as follows :

Bayley Morozewicz

(anal, by Clarke)

SiO 2-16 2-15

A1,0, 1-00 1-00

(Na„KJO -94 -95

The ratios between alumina and alkalies is not as sharp as it
should be, perhaps. If, instead of calling alumina 1, the error
is allowed to rest equally on alumina and alkalies, which|seems
fair, the ratios become :

Bayley Morozewicz

(anal, by Clarke)

SiO 2-21 2-21

AljO, 1*03 1-03

(Na„K,)0 -97 -98

Whichever way ^the ratios are calculated, the value for silica
comes very close to 2*2, which represents the limiting ratio.
The value which we obtained before was 2'21. Since the two
values are practically identical, there seems to be no reason
whatever for modifying our original statement regarding this
ratio. Judging purely by the evidence available, we cannot
agree with Sowen ' that natural nephelites are probably never

It is to be hoped that the problem may be attacked from
the synthetic standpoint in an adequate way. By this
means, it will perhaps be shown whether the saturation limit
changes appreciably with the temperature of formation, and
also whether the potassium content affects this limit to any
great extent.

Chemical and Mineralogical Laboratories of the
Sheffield Scientific School of Yale University,
New Haven, Conn., February, 1912.

♦ Bull. Geol. Soc. Amer. , iii, 231 , 1892. f Min. Petr. Mitt. , xxi, 288, 1902.

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442 A. Ohson-^Ifew Genu8 of Palosechinoidea,

Art. XXXVIII. — Description of a new Oenus and Species of
Palceechinoidea /* by Axel Olsson.

Lepidechinoides gen. nov.

Shape subspheroidal with five arabulacrals and five inter-
ambulacral fields. Ambulacrum consisting of two columns of
alternately arranged plates imbricating aborally. Each of the
ambulacral plates pierced in the middle by a pair of pores set
close together. In addition each ambulacral plate is pierced
on the extreme ventral surface by a single pore situated on the
adjacent ends of the plates. Interambulacrnm composed of six
columns of adorally imbricating plates. Adambulacral plates

Fig. 1.

Lepidechinoides ithcuiensis Olsson.

Fig. 1. Side view of specimen enlarged three diameters.
Nos. 1, 2, 3, 4, 5, 6, indicate number of column. 1', 2', 3', 4\ initial

slightly smaller than the second column of plates and perforated
near ambulacral edge. The interior plates of the interambu-
lacral series more or less hexagonal in shape, except those on
the extreme ventral surface, which are small and ecale-like.
Spines small and striated, dilated at the base.

* The writer is indebted to Prof. H. S. Williams for the many kind sug-
gestions in the preparation of this paper.

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A. Olsson — ^ew Oenv^ of Palmechinoidea. 443

Zepideehinoides Uhacensis sp. nov.

Ambulacra! plates about three to each of the adambulacral
plates bordering them. Each plate perforated in the middle
by a pair of pores set close together. Arrangement of plates
alternate and imbricated aborally. Interambulacrum consist-
ing of six columns of rather large plates imbricated adorally.
Second column of plates larger than the adambulacral plates.
Adambulacral plates rhombic or pentagonal in shape and per-
forated near the ambulacral edge. The inner series of inter-
ambulacral plates more or less hexagonal in shape, except
those on the extreme ventral surface, which are small and
scale-like. These plates pierced in the center except those on
the ventral surface. On the oral surface a few of the ambu-
lacral plates are pierced bj a pore each on their adjacent ends,
but they are confined to this region. Secondary spines small
and striated and dilated at the base for attachment.

Length 2-5<^°^

Width 4^°»

Width of ambulacral area 4™°^

Width of interambulacral area at middle 17"°

After a careful study of the specimen and of the descrip-
tions and figures of the other three genera in the family,
viz. — Lepidocentrus MuUer, Perischodomns McCoy, and
L^idecMnus Hall, the following points of resemblance and
differences were made out. In
the imbrication of both areas it
approaches Lepidechinvs and
Perischodomus and differs from ^^<*8. 2, 8.

Lepidooentrus^ in which the am-
bulacral plates are inflexible.
As in ZepidechintiSy the initial
plate V is retained. It is small
and irregularly foursided, its ^

ventral apex is sharp and does ,<i^^

not appear to have suffered from ^

resorption. This specimen in its

possession of only six columns j^os. 2, 8. Secondary spines

of interambulacral plates is not enlarged ten diameters,
so highly accelerated in its de-
velopment as the genus Lepide-
chinua and the species Lepido-

centrus muUeri Schultze. In Lepidechinus rarispinus Hall
the introduction of new plates is so rapid that each initial
plate touches the next. In Lepidechinoidea the plates 2, 3, 4
and 5 follow each other rapidly, as shown in figure, but between
plates 5 and 6 there are three intervening plates. The exact

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444 A. OUson — New Oenns of Palceechi/noidea.

size and shape of the adambulacrals cannot be ascertained
because of the overlapping of the second column of plates;
they appear, however, to be rhombic or pentagonal in shape
and slightlj smaller than the second column of plates, which
are undoubtedly the largest of the interambulacrals in this
species. The remainder of the interambulacral plates are
mainly hexagonal in shape, quite perfectly so near the dorsal
surface, but on passing ventrally their edges become rounded.
On the extreme oral surface the adambulacral plates are small
and scale-like, closely resembling those of Lepidechi/ixua.
Along a line through the initial plate 4', the diameters through
these plates are as follows : 2-75'"", 4"™, 3"", 3"", 3-75'»'", and
2*75"". The number of columns of interambulacrals is vari-
able even in the same genus and may, therefore, only be con-
sidered of specific value. The list below gives the range of
the number of columns of interambulacrals in the various
species in the genera of the family Lepidocentridse.

(Eu) LepidocentruB rhenanus Schultze 6 I
fEui " mxtUeriBeyrUl

(Eu) " eifilianus MtlUer unknown

(Eu) JPeriachodomus hiserialis McCoy 5 I

" iUinoisensis Worthem & Miller

5 or more I
Lepidechinus rarispinus Hall 111
" imbricatus Hall 8 I

Lepidechinoidea ithacensis 6 I

In the number of ambulacral plates to each of the adambu-
lacrals there is some variation. As could be expected both in
Lepidocentrus and Periachodomus^ in which the adambu-
lacrals are large— being the largest of the interambulacrals —
there are many ambulacrals to each of the adambulacrals,
while in Lepideohinua and in Lepidechinoidea^ in which the
adambulacrals are relatively small, the opposite is the case, as
shown below.

Lepidocentrua rhenanua Schultze 7-8 A

'* mulleri Beyr 7-8 A

" eifilianua MttUer unknown

Periachodomita hiaerialia McCoy 5-8 or more A

*• iUinoiaenaia Worthen & Miller

Lepidechinua rariapinua Hall 3-4 A

" imbricatua Hall

Lepidechinoidea ithacenaia 3-4 A

In the above brief summation of a few of the generic char-
acters, nt is evident that it is fairly close to Lepidechinua Hall.
It has for one of its most important differences the perforation
of the ambulacral plates in the center and not on the distal

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A. Olssmi — Ifew Genua of FalcBechinoidea. 446

end. Any variation in the ambulacral plates is of great
importance and must be considered of at least generic value.
Lepidechinoidea differs also from Lepidechinns in its posses-
sion of fewer columns of interambulacrals and, more impor-
tantly, in having these plates more or less hexagonal in shape
and not scale-like as in the latter genus. Xn this latter char-
acter L^idechinoides appears to represent a more primitive
form. tJackson in his Studies of Palseechinoidea* shows in
reference to Lepidechinus rarispinua Hall, that the rhombic
and hexagonal shape of the dorsal, or newly added interambu-
lacral plates, have phylogenetic significance, having characters
seen normally in less specialized genera and indicating deriva-
tion from forms which did not have imbricating plates.
Moreover those forms with scale-like imbricating plates are
specialized and not primitive types.

From the Devonian of America there are at present three
genera and four species of Palseechinodea, representing two
families Lepidociaaridm Bather {ArchceocidariddB McCoy)
and I^idocentridcB Lov6n. Vanuxem in his Report of the
3d Geological District, p. 184, mentions some doubtful remains
of echinoids from Dryden which he called JEchinua drydenen-
sis. These specimens were later examined by Hall,t who
referred them to the genus Eoddaris Desor. They are
described as being from the shaly sandstones of the Chemung
group, 1,000 feet above the Tully limestone, representing
therefor the Enfield shales of the Portage formation. The
genus Eocidaris belongs in the family LepidocidaridsB and with
Xenoddaris clavigera Schultze of Europe are the only mem-
bers of the family found below the Sub-Carboniferous. The
family LepidocentridcB Loven is now represented in America
by the two genera Lepidechvaus and Lepidechinoides herein
described. Of the genus Lepidechinus two species are known,
viz., Z. rarispinua Hall from the Chemung of Pennsylvania,
and the Waverly group of Ohio and Z. irnoricatus Hall from
the Burlington limestone of Iowa. Lepidechinoides ithacensis
therefore represents the earliest known echinoid from America
although in Europe the genus Bothriocidaris Eichwald, of
which two species are known, is from the Ordovician. The
geological position of all the species in the family Lepidocen-
tridse is shown below :

Lepidocentrus rhenanus Schultze

" mulleri Beyr, middle Devonian of Muhlen-

berg — near Geroldstein Eifel
" eifilianus Mtlller, Devonian of Nohn Eifel

» BuU. Geol. Soc. of Am., vol. vii, p. 228, 1896.

1 20th Annxial Report of State Cab. Nat. Higt. of N. Y., 1868, p. 848.

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446 A. OlsBon — New Oenv^ of Palcsechinoidea.

Periachodomus biserialis McCoy

'' illinoisensis Worthen A Muller Chester lime-

Btone — Pope Co. 111.
Zepidechinus rarispinus Hall, Chemung Penn. and Way-
erly — ffroups of Ohio
" imbricatusHaiW^ Burlington limestone— Bur-

lington Ohio
Lepidechinoidea ithaceuaia Ithaca beds Portage formation

The type specimen herein described was found at the Uni-
vei'sity quarry, sometimes called the McCormick quarry, near
the lower border of the Cornell campus. This quarry is situ-
ated in the zone* characterized by the presence of Spirifer
mesdstrialis and CryptoneUa euaara^ which in the Ithaca
region are rarely found above or below these beds. This zone
is contined to about twenty-five feet in the center of the Ithaca
shale member and of which fifteen feet are exposed in this
quarry. It is made up of hard sandstone layers with few shale
beds. Fossiliferous layers sometimes occur so thickly filled
with fossils as to produce an impure siliceous limestone. On
passing eastward this zone is believed to thicken and to be
represented in the Chenango valley by the Oneonta sandstone,
which there overlies the Ithaca. Besides Spirifer mesa-
strialis and CryptoneUa eudora^ the following fossils are
quite characteristic of this zone : Actinopteria hoydi ; Cama-
rotoBchia eximia ; Leiorhynchua meaacoatale ; Orthoceraa
hehryx ; Gomphocerds tumidum and Stictapora meeki asso-
ciated with numerous crinoid stems.

Those who desire a more detailed comparison of the genus
herein described with the other genera in the family will find
the works listed below to be of service :

Hall. Desc. New Spec. Crin., 1861, p. 18.

Hall. 20th Rep. iN. Y. State Cab. Nat. Hist., 1868, p. 340,

pi. 9, fig. 10.
Keeping, W. Notes on the Paleozoic Echini, Quart. Jour.

Geol. Soc, Tjondon, vol. xxxii, p. 35, 1876.
Worthen & Miller. Geol. Surv. Ill, vol. vii, 1888, p. 333,

pi. 31, fig. 8.
Jackson, R. T. Bull. Geol. Soc. Am., vol. vii, 1896, p. 222-242.
Klem, M. J. A Revision of the Paleozoic Pal»echinoidea

with complete bibliography. St. Louis Acad. Science

Trans., vol. xiv, 1904, pp. 1-98, 6 pi.

Ithaca, N. Y.
Jan. 4, 1912.

* BaU. U. S. G. S., No. 3, p. 17. Watkins Glen-Catatonk folio, U. S. G. S.,
No. 169, field edition, pp. 64, 65, 92, library edition, pp. 6, 8, 12.

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F. H. Lahee — Metamorphism and Geological Stiructure, 447

Abt. XXIV. — Relations of the Degree of Metamoiphism to
Geological Sti^cture ana to Add Igneous Intrusion in the
Narragansett Basin^ Rhode Island ; by Frederick H.

(Concluded from p. 872.)
Part III.


Petrology of the post-Carboniferous rocks.
Basic intmsiyes.

Relations of the minette to the Carboniferous sediments.
Acid intrasives.
^ Introductory remarks.

General and theoretical considerations.
The granite phase.

Relations to the Carboniferous sediments.
The pegmatite phase.
Relations between the pegmatite phase and the granite

Relations of the pegmatite phase to the Carboniferous
The quartz rein phase.

Relations between the quartz vein phase and the pegma-
tite phase.
Relations of the quartz vein phase to the Carboniferous

Relations of the intrusion of the acid intrasives to the f olding,
metamorphismi and schistosity of the Carboniferous
Conclusions to the study of the acid intrusives.
Relations between the minette dikes and the acid intmsives.
Summary and conclusions.

Petrology op the Post-Carboniferous Rocks.

Post-Carboniferous rocks, intrusive into the sediments of
the Narragansett Basin, may be classified from a relative stand-
point as basic or acid. To the former category belong a few
minette dikes ; and to the latter, an extensive series of acid
intrusives ranging from granites, through pegmatites, to quartz
veins.* These we shall consider in the order named.

* Occasional aplite stringers, belonging to this series, cut the granites, and
one or two have been seen to intersect the pegmatite.

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448 F* H, Lahee — Metamorphism and Geological Structure.

Basic Intrusiyes.

Description, — Dikes of minette have been found in southern
Conanicut Island, and of these there are seven instances.* Six
cut the fine greenish schists of the Beaver Tail Peninsula
(fig. 1, Loc. 23, 14:D) and one cuts the pre-Carboniferous
Conanicut granite.

These dikes consist of biotite and orthoclase, together with
some microcline, plagioclase, apatite, zircon, titanite, and the
secondary minerals, chlorite, calcite, epidote, limonite, and leu-
coxene.t The biotite, as noted by Collie and Pirsson, reveals
evidence of two generations. The older is represented by
large idioraorphic plates which are clouded — darsly near the
peripheries, but shading off inward — and which contain very
line rutile needles and leucoxene powder. The nitile needles
are especially abundant near the edges of the plates. They
are arranged in three directions, eacTi at 60° to the others, in
planes parallel to the basal pinacoid of the mica. The leu-
coxene, while sparsely distributed, is more plentiful near the
borders of the mica flakes.

Of the younger generation numerous smaller plates are seen
and also zones which encircle the earlier phenocrysts. This
later form, whether as separate crystals or as border zones, is
clear, greenish, and pleochroic, and contains no rutile nor leu-
coxene. When it occurs surrounding individuals of the first
generation, it is in optical orientation with them. Both types
nave partly or wholly altered to chlorite.

In the section investigated by the writer, there was no par-
allel orientation of the constituents, and evidences of crushing
were slight. In other specimens there is a distinct schistosity.
Pirsson^ attributed the rutile inclusions in the biotite pheno-
crysts to the influence of the forces which produced this
schistosity ; but since the biotite crystals are surrounded by
zones of unrestrained mica and since the orthoclase grains may
abut against or enclose such coated phenocrysts with their
rutile needles, we conclude that the anomalous features
described for the biotite of the first generation were of mag-
matic origin.

— Relations of the minette to the Carhoniferous sediments, —
In some places the minette seems to have been intruded into

* Certain ones of these dikes were described by the following writers in the
works cited : Foerste, A. F., in Geology of the Narragansett Basin, by
Shaler, N. S., Foerste, A. F., and Woodworth, J. B., U. S. G. S.,Monog.
zxziii, 1899, p. 232. PirRson, L. V., in his Geology and Petrography of
Conanicnt Island, this Jonmal (3), zlvi, p. 363, 1893. Collie, G. L., in his
Geology of Conanicut Island, Trans. Wise. Acad., x, p. 199, 1894-1895.
Crosby, W. O., in his Contribution to the Geology of Newport Neck and
Conanicut Island, this Journal, iv, 230, 1897.

f Pirsson gives a chemical analysis : op. cit., p. 375.

jOp. cit., pp. 375-376.

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F, H. Lahee — Metamorphism and Geological Structure, 449

joint planes or along the cleavage of the southern Conanicut
Carboniferous schists. Or, again, the dikes may cut indis-
criminately across such structures. In most cases their thick-
ness is rather variable. Short apophyses may pass from them
into the country rock, and small inclusions of the latter may be
seen. Exomorphically the schists have been somewhat baked
and bleached. The most obvious endomorphic features are
the decrease in size of grain toward the contact and the par-
allelism of the biotite flakes with the walls (flow structure), as
noted by Collie* and Pirsson.f Locally these dikes show some
folding and schistosity. Veins of massive, milky quartz, some-
times of considerable size, intersect them with sharp contacts.

From these petrographic and structural relations, it would
seem that the minette dikes were injected into the Carbonifer-
ous sediments before the period of deformation came to an end,
yet after schistosity and jointing had been developed in the
country rock. J

— Sumina/ry. — Dikes of minette (a) have been found in a few
places in the southern part of Conanicut Island ; (J) are clearly
intrusive into, and are, therefore, later than, the Carboniferous
sediments and the pre-Carboniferous Conanicut granite ; (<?)
were injected during the general period of deformation of the
Carboniferous series; {a) are themselves cut by numerous
veins of massive, milky quartz.

Acid Intbusives.

Introductory remarks. — We have already mentioned the
fact that the granitic rocks in South Kingstown are probably
intrusive into the Carboniferous sediments, and that they are
not pre-Carboniferous as had formerly been supposed. Since
these granites — part of the Sterling series — are especially
prominent on Boston Neck (B : 14 and 15, fig. 1), they may be
referred to as the ' Boston Neck granite.' They appear to be
closely related in origin to the great group of pecrmatites and
quartz veins which likewise cut the Carboniferous rocks.
Herein we shall denote the Boston Neck granite, the pegma-
tites, and the associated quartz veins by the general term,
* Acid Intrusive Series.'§

* Op. cit. , p. 228. t Op. cit.

tPirsson (op. cit., pp. 371-872) said that the schistosity, folding, and
faulting in the dikes were caused by dynamic forces acting along north-south
lines after intrusion. Collie (op. cit., pp. 228-230) stated that the nearly
north-south dikes are schistose because they lie nearly at right angles to the
direction of the forces ; the east-west ones are folded and faulted.

§ Dr. Loughlin, in his ' Intrusive Granites and Associated Metamorphic
Sediments in Southwestern R. I.* (this Journal, xxix, 447, 1910), presents
evidences for the genetic relationship of the granites of southwestern Rhode
Island, the pegmatites, and the quartz veins. From investigations carried
on in the extreme eastern portion of Dr. Loughlin^s area and eastward, pre-
vious to the publication of the paper just cited, the writer had arrived at
similar conclusions, and, certainly in that region where the fields of work
overlap, he is in agreement with Dr. Loughlin.

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450 F. n. Lahee — Metamorphimi and Oeologioal Strtocture.

General and theoretical considerations. — As in the discus-
sion of the structural geology of the Basin (Part I of this
paper), here also we shall put theory before fact. Accepting
the doctrine commonly held to-day, namely, that most peg-
matites are of magmatic derivation,* we shall review below
certain facts which may assist in the determination of the
relations between the Acid Intrusive Series and the Basin

The importance of the role played by catalyzers, or mineral-
izers, in the crystallization of magmas, and especially of acid
magmas, is widely recognized. These miueralizere "have been
defined as volatile substances which, without entering into the
final composition of minerals, render possible or facilitate their
formation and crystallization."! This they do by reducing the
viscosity of the magma and by lowering the freezing-points

of its constituents.^ Barker continues, "There is no

reason for excluding the case in which the mineralizer, or part
of it, enters into the mineral as finally constituted."§ Among
the chief catalytic agents may be cited fluorine, chlorine, boric
acid, carbon dioxide, hydrogen, and water gas.||

* For snmmaries of theories for the origin of pegmatite, see the following :

BrOgger, W. C, Die Mineralien der Syenitpegmatitgange der sudnor-
weg^schen Angit nnd Nephelinsyenite. Zeitschr. ffir Eryst., zvi. I TheU,
pp. 215-226, 1890. Trans, by N. N. Evans, Can. Record of Sci., vi, pp. 8»-
46 and 61-71.

Williams, G. H. , General Relations of the Granite Rocks in the Middle
Atlantic Piedmont Plateau, U. S. G. S., Ann. Rept., xv, p. 657, 1894.

Van Hise, C. R., A Treatise on Metamorphism, U. S. G. S., Monog. xlvii,

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