100 AUSTRALASIAN ANTARCTIC EXPEDITION. 



other than that, under the influence of granitic intrusion, the limestone has, in the 

 zone of most intense action, been altered into an amphibolite. The limestone is found 

 to gradually pass into the amphibolite by the development in it of certain silicates. 



A series of thin sections from a suite of specimens of the amphibolites are examined 

 (p. 103), which are claimed to illustrate the transitional stages of alteration. A 

 significant fact was noticed which was found difficult of explanation on the accepted 

 hypothesis. At one end of the series is a rock containing augite, calcite, and felspar, 

 and at the other end is a rock containing dominant hornblende with plagioclase and 

 subordinate augite. It was found that no passage existed between the characteristic 

 pyroxene of the recrystallised limestone and the characteristic hornblende. The 

 hornblende and pyroxene found together in the one section are fresh and show no 

 alteration of one to the other. The absence of transition is important, and shows that 

 the rocks dealt with are metamorphosed products in which both the augite and the 

 hornblende are primary metamorphic minerals, not secondary one to the other. In 

 metamorphic rocks of basic origin hornblende is frequently derived from the alteration 

 of augite, and in such cases the evidences of direct transition are abundant in thin 

 section. The occurrence is, in fact, highly suggestive of the phenomena of metamorphic 

 diffusion. The so-called gradual alteration may very well be a series of metamorphic 

 diffusion products between the limestone and the amphibolite. Were this same type 

 of argument accepted it could be shown at Cape Denison that amphibolites are the 

 product of alteration of granite. Metamorphic diffusion products naturally show 

 the chemical transition (p. 104), and will also yield an explanation of the microphoto- 

 graphs on Plates XIV., XV., XVI. of the memoir. The chemical analyses are useful 

 to show again the constant features of amphibolites. No. 16 (104) again falls into the 

 same division of the American classification as the typical amphibolite (No. 629) of 

 the Cape Denison rocks. 



With the outlook of metamorphic diffusion one finds no evidence to disprove the 

 theory that along the junction of granite and limestone there has been a later intrusion 

 of basic rock, either in the form of a dyke or a boss. During the subsequent 

 metamorphism of the area the limestone and the basic rock have recrystallised and 

 the granite changed to gneiss. The enclosed fragments of basic rock in the gneiss might 

 well be considered as the torn-up fragments of a possible dyke. The transition of basic 

 rock to limestone is possible under the conditions which give rise to metamorphic 

 diffusion, and the isolation of blocks of an intrusive rock in the intruded rock is believed 

 to be an established possibility. 



If a dyke mass has appeared along the limestone-granite boundary, it is not 

 surprising that (p. 97) among the many inclusions of amphibolite a careful search should 

 only lead to the discovery of one single fragment of coarsely crystalline limestone. 

 Thick bands of hornblende schist, which are looked upon as originally intrusive rocks, 

 similarly appear at the sides of, or within, outcrops of altered sedimentary rock* in 



* British Geological Survey Memoir, 1907, op. oit., p. 238. 



