THE GONDWANA FORMATION 251 



As regards the petrological character of the Beacon Sandstone, Mawson explains 

 that its constitution varies through wide limits "from a nearly pure quartzose 

 sandstone to a highly felspathic arkose, and felspathic garnet and rutile are frequently 

 present as accessory minerals. The cement while usually siliceous is frequently 

 calcareous." Mawson makes the significant remark that " quite fresh felspar grains 

 are not uncommon. These grains are usually much rounded, but a considerable 

 portion are merely sub-angular." Mawson concludes from the fresh state of the 

 fragmental felspars that the Beacon Sandstone was probably laid down under severe 

 climate conditions, that is, the dry conditions which would result through the inter- 

 ception of snow near the Antarctic Circle during a glacial epoch. Under these con- 

 ditions, far south there might be a considerable absence of thaw. Such undecayed 

 felspars are very characteristic of the Permo- Carboniferous glacial beds of Australia, 

 India, South Africa, and South America. As a result of the rare distribution of 

 the calcareous cement of the Beacon Sandstone calcareous concretions are formed 

 in the rock in some places. 



The concretions often contain within themselves much clay as well as cal- 

 careous material. The central portions are but loosely cemented, so that when 

 the outer shell of the concretion is fractured as the result of weatherino; this 

 soft central portion is rapidly removed by erosion, so that the concretions be- 

 come hollowed out into cups. Mawson determined that the calcareous cement 

 in the centime of the concretions for a width of 4 "6 centimetres was in optical 

 continuity. 



In some of the Beacon Sandstone, as in the case of the arkose from the Upper 

 Glacier Depot of the Beardraore Glacier, small garnets are seen to be present in 

 the sandstone. The particles of garnet are about 0'12 millimetre in diameter; 

 rutile needles are abundant. The felspars are chiefly orthoclase, microcline, and 

 anorthoclase. Both muscovite and biotite mica are present sparingly in small 

 particles. " These are usually partly converted into chlorite, and are often much bent. 

 Rutile is present as microscopic hair-like inclusions in the quartz or occurs as 

 isolated grains." 



The analysis of the Beacon Sandstone by Messrs. A. B. Walkom, B.Sc, and 

 G. J. Burrows, B.Sc, quoted at the end of this work, show the Beacon Sandstone 

 to be fairly high in alkalies, the percentage of NagO being 3 "3 3 and that of 

 Kp 2-63. 



As regards colour, the Beacon Sandstone is either whitish to buff or light greyish- 

 brown, but occasionally develops a greenish tint ; this latter is due to the presence 

 of chlorite. Mawson records the fact that "carbonaceous material appears along 

 the bedding j^lanes of some of the specimens from the Beardmore Glacier, just as 

 is the case with some from the Ferrar Glacier." 



As regards the details of the coal seams contained in the middle 300 feet 

 of sandstone with bands of clay shale no detailed section was measured, but 



