PART XII 



REPORT ON THE PETROLOGY OF SOME 

 LIMESTONES FROM THE ANTARCTIC 



(With Two Plates) 

 BY 



ERNEST W. SKEATS, D.Sc, A.R.C.S., F.G.S. 



Professor of Geology in the University of Melbourne 



INTRODUCTION 



About forty sections and eight hand-specimens of limestones were submitted to me 

 for examination by Mr. R. E. Priestley and Professor David. They represent 

 marine shallow-water limestones, some, possibly all, of Cambrian age, and contain 

 Archceocyathince, sponge spicules of colloid silica, etc. Many of the limestones have 

 been subjected to earth movements and veined with calcite and they present interesting 

 examples of metasomatic change, showing all stages of dolomitisation and silicification. 

 Staining with Lemberg's solution and the attack with hydrofluoric acid were found 

 useful in investigating these two changes respectively. 



Examples of regional dolomitisation were noticed, indicating/a shallow-water 

 origin for the limestone. This was confirmed by the presence of detrital fragments 

 of quartz, olivine, etc., in some of the rocks, and by the fact that some of the limestones 

 were oolitic. The oolitic grains show good concentric structures, possibly due to organic 

 tubules; many are dolomitised and silicified, and these show radial structures in 

 addition to the concentric. Some of these superficially resemble radiolaria but are 

 believed to be of inorganic origin. A comparison with dolomitised oolites from the 

 Transvaal has been made. Two limestones, in situ, horn. Farthest South were examined. 

 They contain Archceocyathince, and one of them a greenish material. A chemical 

 analysis of this rock has been made, and an estimate of the composition of the green 

 material, which may be a submarine tuff of an intermediate alkali rock, or may be, 

 since it contains a colourless micaceous mineral, detrital material. 



DETAILED DESCRIPTIONS OF THE LIMESTONES 



No. 8. Limestone Breccia. Cloudmaker, October 12, 1908. (P. 79.) [Erratic) 



The rock is a limestone breccia. Large fragments of a fairly dense limestone, 

 containing no dolomite and traversed in places by secondary calcite veins, form the 

 bulk of the rock. The rest consists of an iron- stained brecciated area, in which 

 angular pieces of quartz and elongated fragments of muscovite are set in a ground - 

 mass of calcite. In some fragments micro- crystalline chalcedonic silica partly 

 replaces calcite. Some calcite veins appear to fill cracks opened since the breccia 

 was formed, since they pass through not only the matrix of the rock but also across 

 the angular quartz fragments. 



II 1S9 -D 



