DISCOVERY 



91 



the fossil evidence has been destroyed. A petrified 

 stem of an Araucaria was found on an island in the 

 Bay of Isles and would point to an age not later than 

 Lower Carboniferous. ^ An examination of some of the 

 slates has been carried out, but yielded no evidence of 

 great importance. - 



With regard to the igneous geology of the island. » 

 two areas were studied. North of Drygalski Fjord, 

 there is an interesting complex consisting of : 



Quartz diorite plug ) Complex system of dykes 

 Two ages of gabbro J (peridotite, vogesite, dolerite). 



A little to the south-east, but forming part of the 

 same area, there are twelve parallel dykes. The lo\\er 

 one of these was reached and proved to be 

 differentiated, gradually grading from wall rock, 

 which was a gabbro, to a quartz diorite, a biotite 

 granite, and finally alaskite. At Larsen Har- 

 bour, which is on the south side of Drygalski 

 Fjord, the rocks were more basic. 



Epidosite (on top) ^ ^ , c ^ ^ u;^ 



^ ^ ^' \ Two systems of dok-utic 



Spihtic lava - , , " 



Gabbro j '^y^''- 



It is believed by the writer that the lavas were 

 poured over gabbro, or, in other words, the 

 gabbro is not intrusive into the lavas. 



The general strike of the rocks is parallel to the 

 longer axis of the island, and the dips are mainly 

 toward the south-south-west. The folding and 

 faulting on the north-east coast are thought to 

 be the result of pressure either from the south- 

 south-west or north-north-east. 



Zavodovski, South Sandwich Group 



This island was not landed on, but the 

 following observations were made from the ship. 



The island appeared to be a volcanic cone 

 rising to about 1,200 ft. At the base there was 

 a compact columnar basalt.'' Above this, a line 

 of red cinder, and above this, rough pahoehoe 

 lava forming the surface. Sulphurous fumes were 

 issuing from cracks in the cliffs at one or two points. 

 The rock fragments brought up by the Kelvin sounding 

 machine confirm the basaltic nature of the rock. 



1 The Carboniferous period is one of the subdivisions of the 

 Paljeozoic period, which yields the remains of the earhest 

 living things. 



2 Dr. G. L. Elles, D.Sc, Newnham College, Cambridge. 



' Igneous rocks are those which have been erupted from 

 below the earth's crust — an example is granite. They are 

 classified according to the amount of silica which they contain. 

 Thus gabbro contains about 50 per cent. ; quartz diorite, 65 

 per cent. " Basic rocks " are those which, like gabbro, 

 contain the least silica. 



* Basalt is an igneous rock. The isle of Staffa is mainly 

 composed of it ; the tall black columns are typical of this rock. 



Elephant Island, South Shetland Group 



The topographical features of this island are those 

 of a dome-shaped plateau, 300 ft. at the rim and 

 rising gradually to 1,200 ft. in the interior. It is 

 covered in an ice sheet. The glaciers appear to be 

 more of the hanging type than of the valley type. 



The observations of J. M. Wordie ^ on the north 

 coast, and our observations at Minstrel Bay on the 

 west coast, would indicate that the northern part of 

 the island is composed of contorted siliceous phyllites.^ 

 The strike of the rock strata is about N. 95° E. with 

 vertical dips. No faulting was observed, but horizontal 

 jointing was commonly met with. 



Fig. I.— m.\p of the qcest's track. 



At Cape Lookout, however, an entirely different 

 set of conditions was seen. There is here a meta- 

 morphic sei'ies, which consists of the following in order 

 from the sea towards the north ^ : 



Quartz hornblende epidote schist. 



^ James M. Wordie, M.A., " S.y. Endurance." 

 6 Phyllite is one of the metamorphic rocks. These are rocks 

 which were either originally igneous or deposited by sedimenta- 

 tion from water, but have been modified by heat or crushing, 

 and differ widely from their original forms. Quartz, horn- 

 blende, albite, etc., are various forms of the element silicon — 

 familiar to us in the form of flint— -in conjunction with soda, 

 aluminium, iron. etc. 



' Dr. C. E. Tilley, Ph.D., Cambridge. 



