316 TECTOxNIC GEOLOGY 



Messrs. Taylor and Debenham from the Beacon Sandstone of the Mackay Glacier, 

 inland from Granite Harbour in South Victoria Land, will no doubt fix the geo- 

 loo-ical horizon more precisely. Tiiis great plateau coal-measure formation has, 

 tectonically at all events, no representative in New Zealand, but is extensively 

 developed in Tasmania, and on the Australian continent. Tlie horizon, however, is 

 represented in New Zealand, but the rocks there instead of lying in broad flat 

 strips, as they do in the great horst of South Victoria Land, are very steeply in- 

 clined, folded, and much altered by metamorphic agencies. So far then as relates 

 to structure, South Victoria Land is, in regard to its coal-bearing sandstone forma- 

 tion, closely related to Tasmania and South-eastern Australia. 



No fossils have been found as yet in the Ross region above the horizon of Beacon 

 Sandstone until the raised beaches are reached. A possible exception to this rule 

 occiu's in the case of some soft fragments of a rock which has the appearance of a 

 glauconitic sandstone found in the moraines of the Nansen-Drygalski Piedmont. 

 These contain traces of radiolarian shells, but the latter are too imperfect to admit 

 of a chronological sequence being based upon their evidence. 



SUMMARY 



We may now attempt to sum up the evidence in regard to the question as to 

 whether the great horst of the Ross region is, or is not, part of the tectonic unit of 

 the South American Andes. 



At the outset the question presents itself, what are the essential characteristics 

 upon which one may depend for determining tlie unity and continuity of any 

 particular mountain chain ? For example, is one to rely mostly on a continuation of 

 the trend lines, on the similarity of tectonic structure, on the similarity of date of 

 formation of the range, on that of the sedimentary rocks composing the range, on 

 that of the eruptive rocks, or on that of the physiography of the range ? There can 

 be no doubt that all these factors help to determine the question as to whether a 

 mountain mass in one part of the world may be considered to be referable to the 

 same unit as that of another mass at some more or less remote distance. 



We have seen that, tested by its petrological characteristics, the horst of South 

 Victoria Land shows more points of divergence than of resemblance when compared 

 with the South American Andes, and even with the Antarctic Andes of the American 

 Sector. In its general absence of folding, as far as at present examined, the 

 Antarctic Horst does not resemble the South American Andes or the Antarctic 

 Andes of West Antarctica. At the same time it must be admitted that in West 

 Antarctica the folds, as described by J. Gunnar Andersson, appears to be mostly of 

 the nature of gentle anticlines and synclines. 



In reference to similarity of sedimentary rocks, we miss in South Victoria Land 

 the considerable development of Cretaceous and Tertiary rocks met with in James 



