SOUTH SHETLAND ISLANDS 



59 



in a short paper, ' Sur la constitution mineralogique des Shetland du Sud ' {sic),' with only exiguous 

 petrographical notes. Four new analyses are given in the 1939 paper of Barth and Holmsen ((4), 

 pp. II, 14, 25). The remaining analysis is a computation made from a Rosiwal estimate of mineral 

 proportions in a quartz-gabbro from King George Island by the writer ((i), p. 65). The two new 

 analyses made for this work are of a tholeiitic lava type from Fildes Strait (p. 44), and of the Recent 

 olivine-basah lava of the Penguin Island volcano (p. 45). Thus there are now available analyses 

 of eight rocks from Deception Island, five from King George Island, and one from Bridgeman 

 Island. 



Table I b. Analyses of igneous rocks from King George Island and Bridgeman Island 



SiO., 

 AlA 



FcaOj 



FeO 



MgO 



CaO 



Na^O 



KaO 



H,0~) 

 CO., 



Tido 



P205" 



MnO 



57-30 



17-97 



2-17 



379 



2-57 

 6-72 



3-25 

 0-96 



4-26 

 0-56 



0-20 



Q 



F' 



M' 

 nak 

 k 



99-75 



17-3 

 34-7 

 48-0 



35-8 

 17-5 



54-9 

 15-6 



5-4 

 7-0 

 27 

 9-1 



2-9 



1-7 



0-7 



II 



loo-o 



10-6 

 34-7 

 54-7 

 42-5 

 27-7 



53-45 

 19-37 

 3-37 

 4-09 

 4-42 

 8-iS 

 3-55 

 1-35 



1-69 



0-66 

 0-04 



12 



13 



100-17 



53-02 



15-57 



4-40 



6-58 



3-93 



8-15 



2-38 



1-68 



(2-02 



jo-so 



tr. 



i-i6 



0-35 

 o-i6 



99-90 



48-26 

 17-42 



3-36 

 5-6i 



8-83 

 11-56 

 2-44 

 0-89 

 0-24 1 

 o-i6| 

 nil 

 1-07 



0-22 

 0-14 



14 



I00'20 



3-8 



38-5 



57-7 

 37-9 

 20-8 



10-7 

 30-9 

 58-4 

 37-2 

 31-6 



-5-2 

 25-0 

 80-2 

 28-6 

 i8-4 



54-24 



17-20 



2-81 



4-98 



5-84 



10-19 



2-91 



0-92 



0-09 



0-91 

 0-09 



ioo-i8 



5-3 

 29-3 

 65-4 

 33-7 

 17-5 



9- 

 10. 

 II. 

 12. 



13- 



14. 



Hypersthene-andesite, Admiralty Bay, King George Island. Gourdon, op. cit. 



Quartz-gabbro, intrusion, Le Poing, Admiralty Bay. Tyrrell ((i), p. 65). 



'Dolerite',1 dike, Admiralty Bay. Barth and Holmsen ((4), p 25). 



Tholeiitic basalt, lava, Fildes Strait, King George Island. New analysis by F. Herdsman. , . , 



Olivine-basalt, lava of Recent volcano, Penguin Island, King George Bay, King George Island. New analysis by 



F. Herdsman. 



Basalt, Bridgeman Island. Gourdon, op. cit. 



X The description of this rock by Barth and Holmsen makes it tolerably clear that it is a porphyritic hypersthene-augite- 

 andesite, practically identical with the rock of the dike in Admiralty Bay described in the present paper (p. 43). As this is 

 a very conspicuous feature in Admiralty Bay, it is very probable that the two specimens come from the same dike. 



The fourteen available analyses are set out in Tables i a and i b in the above geographical order. 

 The von Wolff normative parameters as modified by the writer are also given.- In these O represents 

 the excess or defect of molecular silica, a positive number giving the amount of normative quartz, 

 and a negative figure representing the amount of olivine. F is the percentage amount of normative 

 alkali-feldspar (orthoclase and albite), and M' the combined percentage of anorthite, pyroxene, 



1 C.R. Acad. Set., Paris, ci.viii, 1914, pp. 1905-7. 



2 A full account of this method of calculation will be published as soon as possible. 



