A Record of New Analyses of Tertiary Igneous Rocks (Antrim and Staffa)

A Record of New Analyses of Tertiary Igneous Rocks (Antrim and Staffa)Author(s): Arthur HolmesSource: Proceedings of the Royal Irish Academy. Section B: Biological, Geological, andChemical Science, Vol. 43 (1936/1937), pp. 89-94Published by: Royal Irish AcademyStable URL: http://www.jstor.org/stable/20490427 .

Accessed: 17/06/2014 05:51

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Royal Irish Academy is collaborating with JSTOR to digitize, preserve and extend access to Proceedings of theRoyal Irish Academy. Section B: Biological, Geological, and Chemical Science.

http://www.jstor.org

This content downloaded from 185.44.77.28 on Tue, 17 Jun 2014 05:51:42 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=ria

http://www.jstor.org/stable/20490427?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


[ 89 ]

VIII.

A RECORD OF NEW ANALYSES OF TERTIARY IGNEOUS RIOOKS

(ANTRIM AND STAFFA).

BY ARTHUR HOLMES,

University of Durham

[Read 22 JuNNE; Puiblished 12 NOvEMBER, 1936.]

IN 1932 I

suogested

a new method of attacking certain problemg

of

petrog-enesis, based on the distributioni of Call, Ca -and K in rocks.' During

the course of the investigation then begun-in-collaboration with Dr. F.

Allison -several new analyses of igneous rocks have been 'made. As the

work is still in progress, and some time must elapse before it becomes

expedient to publish the results, it seems desirable to place on record somie

of the new analyses without further delay, so that they may be made

generally available. The four analyses here presented are-all of well-known

rocks belonging to the Britishl Tertiary Province: the basalts of Fingal's Cave

and -the Giant's Causeway; the olivine-dolerite of the Portrushl Sill; and the

rhyolite of Tardree.

Oliv0ie-basalt, 1'ingal's Cave, $tqffa. The analysed specimneni was collected

from the fresh interior of onie of the columns near the entrance to the Cave,

The rock represents the Staffa Type of the Survey (Mull Memoir, p. 145).

A?ter ' brief pettological desetiption of the rock, Thomas adds (p. 146),

"Tfr4 Staffa type of basalt is essentially a fine-grained olivine-tholeiite, and,

if it *ei4 nore coargely crystalline, it would agtee closely with the Salen Tyyk of tholeiit."

1 Geol. Mag.^ 1932, pp. ?550-552.

PROC. R.I.A., VOL. XLIII, SECT. B. [P]



90 Proceedings' of the Royal Irish Academy.

OLIVINE-BASALT, FINGAL'S CAVE, STAFFA.

PERCENTAGES, MOL. PROPS. NORM.

SiO2 46'70 '7776 Orthoclase . .4 68

A1203 14 66 *1438 Albite .18'74

Fe403 2-75 *0172 Nephelite ...75

FeO 8-75 '1218 Anorthite ..27 06

MgO 7-38 '1830 ( CaSiO, 13'87')

CaO 12'52 *2233 Diopside MgSiO3 8'23 . 27 06

Na2O 2'38 '0384 1 FeSiO3 4'96)

K20 '79 .0084

H20 + 1-59 Olivi Mg2SiO4

7 10

H20 - '83 - Fe2SiO4 4 71 ' .

C02 '10 '0023 Magnetite .410

TiG2 1-72 '0215 Ilmenite . .326

P20, '23 '0016 Pyrite '10

S '05 '0016 Apatite . .50

Cr2O3 '07 '0005 Calcite .23

V203 '04 '0003

NiO n.f. 98'29

MnO '14 '0020 Water 2-42

SrO '05 '0005 BaO '03 '0002 100'71

Auvernose (III, 5, 4, 4)

100:78 Less 0 '02 Analysis by Messrs. Imperial Chemical In4us

tries (Fertilizer and Synthetic Products),

100 76 Ltd., Research Department, Billingham, Co. Durham.

Of the rock from Staffa itself, the only analysis which has hitherto been

available is one by Streng, dating from 1853 (Mull Memoir, p. 17, An. 11).

Though incomplete, Streng's results faithfully bring out the relatively high lime and magnesia which characterise the olivine-basalt of Fingal's Cave as

compared with other analysed examples of the Staffa and Salen types.

Basalt, Giant's Causeway, Co. Aitrim.-The analysed specimeni was collected fromi the fresh interior of one of the columns just outside the

railings at the entrance to the Causeway. In the Mull Memoir (p. 146) it

is inoted " that the Staffa Type includes the columnDar basalt of the Giant's

Causeway." It should therefore be pointed out that the rock, though

otherwise like the Staffa Type, is characteristically very poor in olivine. The relatively lower magnesia and higher silica recorded in the older and



HoLMEs-New Analyses of Tertiary Igneous Rocks. 91

less complete analyses2 are confirmed by the new fiaures. Chemically the rock closely resembles the Brunton Type of tholeiite from Bingfield and the quartz-dolerite of the Whill Sill.3 It is a typical representative of the Non-porphyritic Central Magma Type of the Survey (Tholeiitic Macma Type of Kennedy, An. Journ. Sc., (5) xxv, 1933, p. 240).

BASALT, GIANT'S CAUSEWAY, Co. ANTIIM.

PERCENTAGES. MOL. PaOPS. NoRM. SiO2 50-36 *8385 Quartz . . 146

A1203 14-51 '1423 Orthoclase. . 584

FeZO3 2'61 '0164 Albite . .20-97

FeO 8-09 '1126 Anorthite . .25'53

MgO 6 26 '1553 (CaSiO2 10'35

Cao 10'77 *1921 Diopside . - MgSiO3 5'82 ' 20'27

Na20 2'48 '0400 FeS03 410 J

K30 '99 '0105 ( MgSiOa3 977

H20 + 1.10 - FeSiOs 6 86 J

H20 - 1'27 - Magnetite. 389

C02 '10 *0023 Ilmenite. 202

TiO2 1'06 '0133 Pyrite .11

P205 '45 '0032 Apatite .99

5 *06 *0019 Calcite .23

Cr2O3 *02 '0001

7203 '04 '0003 97'94

NiO nf. - Water 2 37

MnO '12 '0017

SrO '05 '0005 100'31

BaO '03 '0002 Auvernose (III, 5, 4, 4),

100'37 Analysis by Messrs. Imperial Chemical Indus. Less 0 '02 tries (Fertilizer and Synthetic Products),

Ltd., Research Department, Billingham, 100 35 Co. Durham.

Part of the same analysed specimen has also been analysed by Hevesy and Hobbie for lead.4 The amount present was found to be Pb = 4 x 10-6 gm.

per gm., slightly less than the average amount in a composite of 67 saniples of gabbro (5 x 106), and very mnuch less than the amount found by Smythe?

in a comnposite of 2,950 samples of the Whin Sill (24 x 10-6).

2 ?. Streng, cited in the Mull Memoir, p. 17, An. A.

T. V. M. Bao, "A Study of Bauxite," Min. Mag., xxi, 1928, p. 414, An. I. s A. Holmes and H. F. Harwood, Min. Mag., xxii, 1929, p. 23. 4 G, Hevesy and B. Hobbie,

" The Lead Content of Bocks, "

Nature, exxviii, 1931, p. 1039.

5'J, A. Smythe, " A Chemical Study of the Whin Sill," Trans. Nat. Hist. Soc. Northumberland,

Durham, and Newcastle-upon-Tyne, vii, 1930, p.-34.



92 Proceedings of the Royal Irish Academy.

Determiniationis of uraniium and thorium in the basalt of the Giant's

Causeway are as follow, the figures being in units of 104 gin. per gm. of rock.

Corresponding results for the olivine-basalt of Fiingal's Cave are added for camparison

URANIUM. THoRIUM. ANALYST AND REFERENCE.

: 152 R. J. Strutt, Proc. Roy. Soc., A, lxxvii, 1906, p. 479,

Giant's Causeway 1-44 17 J. H. J. Poole and J. Joly, Phil. Mag. (6),

xlix, 1924, p. 826.

Fingal's Ctve 2-82 9-0 Ibid.

These figuires are of interest in association with the lead content. since they show that, even if the -material of the Gianit's Caauseway basalt had

existed for 1,600 miiillioin years, the accuimulated radiogenic lead would liave

amounted to only 0-5 x 10-' gin. per gm6 Clearly the prbportion of lead

isotopes genlerated from the radioactive elements during geological time is small coimpared with the lead origrinially present. The total ainount of

lead, now present is 300 to 400 times as nmuich as can have been generated

in the material since it becanme the rock of the Causeway. I have takell the

opportunity of mnenitioining this nmatter because 1 am sometimes asked if

the lead-ratio method could Inot be applied directly to measuling the ages of

igneous rocks. The above data show that nlo such applicationi is practicable.

Olivine-doterite, Portrush Sill, Co. Antrim. The analysed specimen was collected by Mr. N. Harris from Kerr Street Quarrv, Poitrush, frormi a level

about six inches below the roof of the sill. It represents a variety which is

tranisitional between the filie-grained nmargin anid the coarser characteristically

mottled rock which miiakes up the bulk of the intrusion. The specinmen was

chosen for a'nalysis because in its modal comipositionl it closely corr'esponds to

the average for the whole of the -sill, as exposed. The miinierals present are

plagioclase, graniular pyroxene, olivile, magnetite, and a little initerstitial

thomisoniite. A detailed account of the petrology of the Portrush sill will

appear in a forthcomlingo paper by Mr. Harris. Chemically the rock -is akin

tb the Plateau. Magmna Type of the Survey (Olivine-basalt Magma-Type of

Kennedy, loc. cit.), in which respect it resembles the Lower Plateau basalts

of Alntrim, anid stanlds in conltrast to thle rock of the Giant's Causeway,

whTilfiWth& ft f4dFtlfe= Upper Plateau flows. 'Th }e relatively high content -of

copper is of geochemical interest.

Rhyolite, Ttardree Mountdin, Co. Antrirn. The analysed specimen is of the

enidely toluinnar3-grey, porphyrit,ic variety fron -the quarns of T'ardree

6 For other examples see A. Holmes, Nature, exxviii, 1931, p. 1040.



HOLMES-New Analyses of Tertiary Igneous Rocks. 93

Mountain. A description of the rock, with an incomplete analysis by Player,

is given by Teall.7 For additional details reference may be made to the later

descriptions by Cole8 and Watts?9

OLIVINE-DOLERITE, POInTmRUSH SILL, Co. ANTRIM.

PEOCERNTAGES. MOL. PROPS. NORM.

SiOs2 46'51 '7744 Orthoclase - 4 23

A1203 15'60 '1530 Albite . . 15'78

Fe2O3 '99 '0062 Anorthite . . . 32-10

FeO 9-14 '1304 Halite . . , 05

MgO 9'05 *2245 CaSiO3 9'48

CaO 11'77 '2104 Diopside MgSiO3 5 33 18'57

Na2O 189 '0305 FeSis% 3'76 J

K20 *72 0076 MgSiO3 3'26 HIyperathene t5-46

H20+ 1'79 ypee FeSiOs 2-20

It20- 75 Mg2SiO4 9.77

002 '07 0016 Olivine Fe2SiO4 7'25 17'02

TiO2 84 '0105 Magnetite . . 1-46

P205 '52 s0037 Ilmenite 1 59

F '04 '0021 Pyrite . , . '28

Cl '04 '0011 APatite . . 1'24

S *15 '0047 Calcite . * . 16

Cr2O3 '02 '0001 97.94 Water . . . 2'54

V203 '02 '0001

NiO '07 '0009 100_48

O1O '15 '0019

MnO '16 '0023

SrO '02 '0002 Auvernose (III, 5, 4, 4)

BaO '04 '0003

100'35 Analysis by Messrs. Imperial Chemical Less 0 '07 Industries (Fertilizer and Synthetic

Products), Ltd., Research Dept., Bil 100'28 lingham, Co. Durham.

i J. J. H. Teall, " British Petrography," 1888, p. 348. The analysis by Player is repeated in

Washington's Tables, 1911, p. 971. 8 a. A. J. Cole,

" The Bhyohtes of the County of Antrim," Trans. Roy. Dublin Soc vi 1895 p. 77.

" '

G-. A. J. Cole et aliter, "

The Interbasaltic Bocks of North-East Ireland," Mem. Geol Surv. Ireland, 1912, p. 93.

9 W. W. Watts, "Note on the Occurrence of Perhtic Cracks in Quartz," QJGS 1 1894 p. 367.

* ? ?

PROC. RJI.A., VOL. XLIII, SECT. B. [Q]



94 Proceedings of the Royal Irish Academy.

RHYOLITE, TARDREE MOUNTAIN, Co. ANTRIM.

PERCENTAGES. MoL PROPS. NoRM.

SiO2 75-80 1P2621 Quartz 44-21

A203 12 45 *1221 Orthoclase 24 6&

Fe203 1V47 *0092 Albite . . . 19-45

FeO *44 *0061 Anorthite . . . 4 95

MgO '08 *0020

CaO 1'00 *0178 Corundum . . . 2'3&

Na2O 2'30 0371 MgSiO3 . . . 2

K20 4'17 -0443

H120 + 1'30 - Magnetite . . . 1-41

H20- 80 -- Hmatite . . .50

CO2 none 97& Water . . 2'10

TiO2 tr. 99'80

P205 tr.

S , tr. Tehamose (I, 3, 2, 3)

MnO none

9-81 Analysis byj-W.

H. Herdsman.

ACKNOWLEDGMENT.

In conclusion I wish to express my grateful thanks to the Research

Department of Messrs. Imperial Chemical Industries, Limited, not only for

a research grant out of which the cost of these and several other analyses has

been defrayed, but also for permission to have some of the analyses carriedc

out by the staff of their Analytical Laboratory at Billinrgham.



Documents

A Record of New Analyses of Tertiary Igneous Rocks (Antrim and Staffa)