126 THE VOYAGE OF H.M.S. CHALLENGER. 



colour. The concretionary structure and brilliant polarisation colours distinguish it 

 clearly from chabasite. Felspar alone is usually found retaining its natural colour ; 

 augite is transformed into delessite or grengesite, and the olivine is covered with oxide 

 of iron, or even filled with hematite, or else serpentinised. Chabasite, the rhombohedric 

 forms of which are visible to the naked eye, fills all the vesicles with closely-packed 

 grains. These react feebly between crossed nicols ; they show striations and twinnings, 

 and the other phenomena which have been particularly studied by Professor Becke. 



Professor Roth's lithological observations on the rocks of Betsy Cove go to show 

 what a large part doleritic basalts containing zeolites play in the whole peninsula. 

 We need refer to a few only of the rocks of another nature which he has determined 

 from specimens collected by the German expedition. A rolled pebble of red porphyry 

 was found at the foot of Mount Peeper, and this, according to our author, seems to prove 

 the existence of ancient rocks in Kerguelen. We shall refer to this point again. The 

 specimens from the eastern part of Mount Peeper have been found to contain half-fused 

 fragments of sanidine rock. This clearly proves that the trachytic masses existed prior 

 to the basaltic eruption. This conclusion will be confirmed by considering the relation 

 between the sanidine rocks and the basalts of Royal Sound and Greenland Harbour. 



Professor Roth records from the neighbourhood of Mount Crozier, besides the usual 

 eruptive rocks of Kerguelen, fragments of a bluish grey sedimentary rock, the age of 

 which cannot be determined. It is related to a labradorite-porphyry coming from the 

 south-western extremity of Lake Margot. This rock is compact, and the greyish blue 

 ground-mass contains triclinic felspar and grains of pyrites, its appearance recalling the 

 rocks of ancient type. The specimen effervesced strongly with cold acids, and after treat- 

 ment with hydrochloric acid the ground-mass appears lighter in colour, while the felspar 

 crystals are much corroded. Microscopic preparations show that the ground-mass is 

 much decomposed, and contains triclinic felspar, a chloritic mineral probably derived 

 from augite, altered olivine, and magnetic iron. Another rock, coming from the series 

 of hills in the Studerthal, to the north-east of Mount Crozier, has a granular structure, 

 and contains chiefly triclinic felspar, plates of black mica, and an altered mineral pos- 

 sibly derived from hornblende. The rock effervesces slightly in acids. It appears to 

 contain some crystals of orthoclase, and Professor Roth was led to class it with the 

 ancient eruptive rocks such as micaceous diorites. 



The great peninsula, the rocks of which have now been described, is bounded on 

 the south by a large bay, Royal Sound, occupying the south-eastern extremity of 

 Kerguelen. Here the British and American stations 1 were situated in 1874. Before 



1 The American transit of Venus mission was established at Royal Sound, near Molloy Point. Dr. Kidder, the 

 medical man of the party, has published his botanical and zoological observations in Nos. 2 and 3 of the Bulletin of the 

 United States National Museum, Washington, 187C. 



