DENSITY OF IRISH ROCKS The densities of 157 rock specimens :in the Geophysics Labora­ tory of Trinity College, Dublin, have been determined to provide data for the . evaluation and interpretation of the gravity survey of Ireland. These rock samples have been collected at various times for different purposes, but, in the main, are fairly repre­ sentative of the rock types occurring in this country. The average size of each sample was about 25 ccs. and its density was deter.mined with a Walker Steelyard Balance, weighirigs being taken in air and in wate~. Most of the samples were imper­ vious to water and, apart from ensuring that all air bubbles were eliminated, no special efforts were taken to ensure that they were saturated.. Sandstone specimens, especially of Triassic age, were the most difficult to measw-e since they tended to break down in water. In these cases the weighing in water was carried out after the removal of all loosely attached grains and, if a second weigh­ ing in water was necessitated by further loss of loose grains, this weighing was carried out after drying in air overnight. This procedure was repeated until satisfactory readings were obtained. Highly vesicular specimens were boiled in water for five minutes · and allowed to cool in cold water before the weighing in water. This method, though satisfactory with porous rocks, was inevitably unreliable when applied to specimens which were both vesicular ii In the table the reference number is that in the catalogue of the Geophysics Laboratory at Trinity College, Dublin. The locality given is intended only as a guide. The geological age of each specimen -is shown but in some cases this is uncertain and indicated by a question mark after the name of the system. In a few instances the age is unknown. I wish to thank Professor J.H.J. Poole for the use of a Lab- oratory and for permission to use the late Professor J. Joly1s basalt samples, and Professor L. B. Smyth for the loan of the Steelyard Balance. The work was made possible by a grant from the Meteorological and Geophysical Department of the School of Cosmic Physics in the Dublin Institute for· Advanced Studies. J. S. JACKSO ' ' 'I I . DENSITY OF IRISH ROCKS -- .... ..... -· .. i:ii ~ ... - - . - ----- ~ County Class Ref • Rock Type : Locality Geological Age I I I 5/ '-'!U ;. Antrim I Igneous I B.l Basalt The Maidens Eocene -· 2.98 ~ B.2 Basalt Giant's Causeway Eocene ~ 2.83 B.6 Columnar basalt Giant' s Causeway Eocene 2.82 B.ll &salt Rue Point,Rathlin Is. Eocene 2.81 B.l3 Dolerite Ballycastle Oligocene? 2.99 B.l8 Basalt Ferris Point, Larne Eocene 2.79 B.l9 Eg,sa:!.t Black Head Eocene 2.75 B.20 Basalt Rathlin (west) E.o cene 2 .. 83 B.22 Basalt(amygdaloidal) Cave Hill, Belfast Eocene 2 0 82 W. 8 Olivine dolerite North Star dyke Oligocene? 2.96 near Ballycastle Sediment ary I W. 5 I Tuff (very Fair Head, Bally- I Carboniferous I 2.56 u weathered) castle W.23 I Chalk Cave Hill, Belfast I Cretaceous 2.59 R.23 Limestone (very Beside North Star Carboniferous I 2.68 u fossiliferous and dyke near Ballycastle slightly weathered) Metamorphic I W. 4 I Hornfels (Lias clay} Portrush I Jurassic 2.70 .6 Homfels ( Carboni- Lough Doo, Fair Head, Carboniferous I 2.72 ferous shale) Ballycastle Igneous I B.21 INewcy Granite Goraghwood Quarry I Devonian 2.69 B. 34 Newry Granite Goraghwood Quarry Devonian I 2.71 (typical specimen) -. - - -J'"" I Carlow I gneot'.S ~ 2.68 ·.. W.20 Mt . Leinster Granite Scallagh Gap I Devonian I - Cavaii - Igneous - . ~:::: B. l5 Basalt .. = .., n !ml. S. E. Kingscourt ITe rtiary, 2.75 Eocene? I I .... - - - < - ............. :-. .-""" DENSITY OF IRISH : --- -• . Densi~y Rock Type !i=~ Locality ·;; I Geological Age I County I Class I Ref. I I g/cm - Tertiary; ,./ I 2.~ Cavan l Igneous I B.49 !Basalt IShot-bor:ing "J" (contd.) (1939), Kingscourt .Eocene? B.50 Vesicular Basalt Shot-boring 11 JX 11 Tertiary, I 2.62 u (1939), Kingscourt .Eocene? W.l I Basalt I Shot-boring 11C11 Tertiary, I 2.82 (1939), Kingscourt Eocene? W.l5 I Crossdoney granite J Crossdoney, Devonian? I 2.67 near Mountnugent Sedimentary I B.37 I Sandstone (M. G.) I Ardagh, near I Carboniferous I 2.52 Kings court W.21 I Sandstone (NRS) I Glacifluvial deposit,l Triassic I 2.31 u 1m1. S.E. Kingscourt W.28 I Gannister (slightly Corratober Bridge, I Carboniferous I 2.60 carbonaceous) near Kings court (C.M.) Cork I Sedimentary I W. 9 I Sandstone (ORS) Rathcormac, I Devonian I 2.67 near Middleton W.lO I Grit I ~. N. Ballydam, I ? I 2.62 near Middleton W.ll I Sandstone ( ORS) I Ballinaclashy Bridge, I Devonian I 2.70 near Middleton W.l2 I Limestone I lml. S. Ba.llyedmond I Carboniferous I 2.74 House,near Middleton ~ ~ 2.66 Donegal Igneous . : B,8 Amorphous quartz Tory Island Dalradian? IDalradian 2.64 IB.9 Amorphous quartz Tory Island . .. : _ ~ l _ - .·::. ,='---"'_-~ B.l2 Granite (rolled Arranmore Dalradian I 2.58 u and weathered) - - - 2.69 u I: - :;:..;-_ B_l..':\ I weathered) Fanad Point Dalradian ~~ I f!'~~!~~ly I :--..:::~ I I I I\) ---.--o, DENSITY OF IRISH ROCKS continued - :.....:;, -~.~ - -:" ;:=:r;~,, r···- .... ~ Density Geological Age County I Class I Ref. Rock Type locality g/cm3 ~ Porphyritic Felsite Near Treantaboy Dalradian 2.95 Donegal ~ Igneous I W.50 I (contd.}" R.37 Diorite !ml. N.E. Mullaghfin Dalradian 3.00 Metamorphic I R.6 Limestone Schist Near Lissinisk School' Dalradian 2.72 R.1.4 Gneiss 2!mJ.s. W. Treantaboy Dalradian 2.95 R.30 Metamorphosed Breen (village) Dalradian _ I 2.71 limestone Dovn 1 Igneous 1 R.45 I Dolerite I Scrabo Hill I l'ertiary, I 2.95 Eocene? Sedimentary I R.5 I Sandstone ( NRS) I Quarry near Lough I Triassic I 2.34 Moronay, near Scrabo Hill R.l? I Mudstone I Quarry near Lough I Triassic I 2.59 Moronay, near Scrabo Hill R.221 Sandstone ( NRS) I Scrabo Hill I Triassic 2.23 R.24 Sandstone (NRS) Quarry Comer, Triassic I 2.45 near Scrabo Hill 2.45 R.26 I Sandstone and Marl I Scrabo Hill I Triassic , R.31 • Grit F.den Fann, Triassic I 2.72 near Scrabo Hill lletamorphic Slate Hill 2.76 I a.uj - INear Scrabo ISilurian R.39 Slate Near Scrabo Hill SUurian I 2.72 2.65 8.3 Granite Bohemabreena Devonian B.? IGranite {weathered) IBohemabreena IDevonian 2.59 u • ;-:: ..... ;; 1-:-- •...:.:-:...::-::; I 1 B.lO Granite (weathered) Rockabill (Is.) Devonian 2.60 u ~- diorite Ordovician 2.99 I ~- _:; -"!:1 ·:._ 1 B.l4 Porphyr1tic Bohemabreena I -. v.> DENSITY OF IRISH ROCKS - continued - Density County Class Ref. Rock Type locality · Geological Age gjcm3 - Dublin Igneous B.24 Rhyolite Blackchurch Ordovician 2.64 (contd.) B.33 Porphyrite Portrane Ordovician 2.86 W.7 Porphyrite Bohernabreena Ordovician 2.95 Sedimentary B.27 Tuff Shennick Is.,Skerries ? 2.~ W.43 Sandstone (ORS) ~. S. of Donabate Devonian 2.67 R.4 11Calp" South of Rush Carboniferous 2.65 R.lO Conglomerate Shennick Is.,Skerries Carboniferous 2o7S R.l5 Sandstone Shennick Is~,Skerries Carboniferous 2.59 R.l6 Shale Shennick Is.,Skerries Carboniferous 2.$2 I I R.25 "Lane" Conglomerate Between Loughshinny Carboniferous 2.76 i and Skerries ~ R.27 Limestone Loughs hinny Carboniferous 2.67 R.29 Conglomerate Between Loughshinny Carboniferous 2.69 and Slrerries "' - R.34 Conglomerate Near Rush Carboniferous 2.70 R.36 Limestone with band Between Rush Carboniferous 2.6$ .. .... of chert and Loughshinny R.3S Gritty Limestone Kate Rock, North Carboniferous 2.67 -. _. of Rush Harbour - . •' 11 11 -. R.40 Carlyan limestone N. of Rush Harbour Carboniferous 2.71 ... ..;.:_ R.44 11 HolJnpatrick" Holmpatrick,Skerries Carboniferous 2.72 . ... ...... - ·-... ...... - limestone ·--.--I '~- " ·~ --'- .. ~ ..... ..._ . -··•"'. _ ..... .... .. -· .. Meta.IOOrphic W.39 Granitic gneiss South side of Devonian 2.65 M-· --, -,, . - - - -L' .. ':. ... G1encree valley ~·- B.16 Slate Bohernabreena Ordovician 2.62 -.··- - .. - . ~ - .. ..._ -.- - : B.17 Mica-s.chist Bohemabreena Sllurian 2.66 ........ - ". 7~-·. W.2 Subsequent do1omitie - - ~- - ·-' Howth Carboniferous 2.71 -. - . - limestone -1="- . --- ...: I . .. -- - - - ·- DENSITY OF IRISH ROCKS continued -~-"'-- ~ ""'!..~ --- -· - ._ __ - - ----· __. - -- .... _._ -.. 1 ... ·r-.....-- -------·--~-' Density County Class I Ref. I Rock Type wcality Geological Age I I I g/cm3 Dublin I Metamorphic I W.141 Quartzite I Howth Head I Cambrian? {Bray 2.65 ( contd;) Howth series) R.32 Dolomitic limestone Lime-kiln Cove, Carboniferous t 2.76 near Loughshinny S.E. of Rush R.351 "Rush" Slate Carboniferous I 2.70 Galway I Igneous I B.23 Porphyritic Galway Bama Pre-Cambrian, 2.66 granite Dalradian? B.26 I Porphyritic Galway Inishlackan, Pre-Gambrian, I 2.6B granite Rounds tone Dalradian? B.39 I Microgranite Rounds tone Pre-Gambrian, I 2.60 u (slightly kaolinised) ·: Dalradian? B.4l I Gabbro Between Ballynahinch Pre-cambrian, I 2.92 and Roundstone Dalradian? Metamorphic I B.421 Hornblende-schist I Letterdyfe Mountain, Pre-cambrian, I 2.99 Rounds tone Dalradian? · W.lB I Crystalline merble I Ballynahinch, Pre-Gambrian, I 2.72 near Roundstone Dalradian? W.l9 I Serpentine I Barnaoran quarry, Pre-Gambrian, I 2.61 ( "Connemara marble") Owenglin River, Dalradian? near Ballynahinch Kerry I Igneous I W.45 I Felsite I Bennaumore Mountain, I Devonian I 2.62 near Lough Guitane Sedimentary I B. 36 I Sandstone ( ORS) I Lough Currane, I Devonian I 2.69 Waterville W.31 I Sandstone (ORS) I Lough Guitane, I Devoni.an I 2.6B near Killarney I I I VI DENSITY OF IRISH ROCKS - continued Density Ref.