Extracto del Periódico Extra a Carlos Mata, presidente de la Junta de Pensiones y

Gxtr&mely variable* but they ore a convenient woy of illustrating the

sort of aasomblagos found vrithin thean#

Riaturos of the constituent imnerols are described below:

Galcito and dolomite: TIze matrix of ihe mazblos is a faiiOy even"* gmi^ied mass o f ciy sta llin e ca lcite and dolomite grain si^es ranging up to 2,0 mm, * vdiich post~o% yetalli^atlon oiuedilng has often reduced to

a veiy fin e ly grmmlar mass, This omshing i s often confinod to certain nozyow bands but sometimes a ll the carbonate within tlio area of a tliin-

section has been aifeoted, The oüier constituent miuoz^s of tlie m&rble also tend to be fragmented along bands of ozuehing but they ore seldom as fin ely m illed as tlio carbonates. In sim ilai' zooke in South Harris*

Davidson was able to distinguish between ca lc ite and dolomite in tliin^seotion for the ca lcite grai.no wera "noazly always clouded and tuxbid wit3i a fine* indeterninate* opatjuc, brmm dust*\ vM le the dolo^ W.te was *^llmpid and frequently id icb lastio to the calcite**; but no such d istin ction has been observed betvmen the two minoiYdo in Wio present case.

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However, staining v/lth solution roveals that oalcito is the

dominant oaz1)onate minoi'al and that both have been mibjectod to gronul**' ation, the oaloite boing genorolly more fin e ly m illed than # 1 0 dolomite;

Amphibole; An amphibole, v^hioh is often oolouzloas in section but oooaeionaOJy has a pale yeH o#ah tint* ooouis in vezy variable amounts, in tliG maiblOk I t forms fresli* xenoblastio* - somotimea. aub-^roundecl grains ifiiidh often w ap around fo r sterlte grains* Tho anplilbole hoe tlie follow^ jjqg optioal proportî^es, +21T 75^, If cKL.1»627 end If Y 1,8*6* These prop*» orties are close to tlioso o f sim ilar aaiphibole ooonrring in t)ie czys** taH ine limestone o f üouth Harris whidi also wraps around fo r ste iite grains and proved, on analysis* to be an unusually llmo^rioh par-» gosito (Davidson, 194;3)*

jg'orstoid.te: This mineral oooura in the mazbles in amounts vozying fraa less tiian one per cent up to about ten per cent of the to ta l volume* I t is colourless mid fom s grains, mostly in Ü10 0#^5 to 2,0 mm, sise

rango, viiicli sliow a ll stages of replaoement by sezpontino fmm slig h t to oonipletG and, as mentioned above, are oooosionally mantled by amphibole. The optic angle, i SV, of the fo rsterlto ranges frcm 82^ to 86^#

I^OKOpite; Phlogopite occurs fa irly abundantly in ciuahed bands

:in tho maibles but is general3y sparise in the unciushed porLions* I t io geneiul]^)" pleochroio v&th X colouzdesn, Y tmd 21 pale yellovdsli broivn,

and forms slender laths some 2,0 to ^,0 m i, in length \ihich may occur sing]y or in clustezt), These laths aie often tiTisted and contorted and

Biopnidat Blo|>s:ide i s absent or sparse In moat of tho maibloo but oo.ooxn.Qm3, bmxls ooiitahi Intezgrowth'o of diqgsido and pazgasite,

dlopaido i s fre d i and coXourlCBs, and forms xenobla^tlo to occasionally

sub-idloblastio grain s,

Bpinc?X.g SpiiieX oooiws In only one of tho # l n sections of marble

ozminod, raiera i t fo%$m oooasional colourless, sub-zwnded grains* 0,5

to 1,0 mm, in ciiajïîotez', oroR^sed by irre g u la r cracks.

Irregular

gv&im

of graphite occur occasionally* and tîic oarushcd bands often contain some

iodotem p late fin e grained opaque im tezdal,

The mineral, assemblages those bands of marble, namely oaloite*

dolomite* %)argesito* fo r ste r ite , phlogopite* and minor amounts of ore* spinel and grvzp3iite, are silmilar to those \dilcb. havo been noted as trie pzWuotE^ of higîi grade z^gional metamozphism o f dolomitio limestone from many parts o f the m ild (Adams and B^urov/, 1910* Davidson^ 1945# Tilley*

1920) and i t seems lik e ly that the original material of the sediment

oould supply tlie constituents necessary fo r the genesis of those minera3.s,

(o) Galc->silicate rocks.

The oalc^^silioate zooks arc lig lit gzey in colour and foim bands up to alxjut t^?en.ty fe et wide vhioh have vezy irregul.ar weatheresd surfaces and thin* often contorted* bedding, The irregular weathered surface typical of tlieso rooks i s illu stra ted in Plate 17# The calc*.^silicate rooks axo intefbanded v/ith tind grade into the marbles but* as stated

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at Una Cott ahoviae the •xm^ilar eeaUwxiag mnrfaoe %yploal of this type.