Appendix I: Geological Observations

by G. Vibert Douglas, M.C., M.Sc., Geologist to the Expedition

As planned by the late Sir Ernest H. Shackleton the voyage of the Quest to Southern Regions was intended to explore the coast from Enderby Land westwards to Coats Land, a length of approximately 2,500 miles. On the routes to and from this main objective it was his intention to call at many seldom-visited islands in the Atlantic, Southern, Indian and Pacific Oceans.

A part of the second objective was attained, and the reader who desires to learn of the detailed geological results of the expedition is asked to consult the full scientific report which is now being prepared, and which, by the courtesy of the authorities of the British Museum of Natural History, is to be published as one of their Memoirs. It is the purpose of the writer in these notes to give an outline of the general geology of the islands which were visited. The names given to the rocks are only field terms, as no microscopic examination has been made up to the present.

Methods Employed

It was found to be seldom possible to do accurate and close geological mapping, owing to the limited time that was available for work ashore. Maps of the areas had to be made, as those of the Admiralty are of too small a scale to do more than provide a skeleton upon which the larger scale sketches can be based. The sketches were generally the result of a rapid reconnaissance with plane table or compass and pace, or in some cases simply a freehand sketch from the summit of a ridge.

Wherever possible hand specimens were collected and the general geological associations noted.

The order in which the following islands are described is not that in which they were visited, but they are grouped as follows:

Islands of the Southern Ocean { South Georgia (68)
{ Elephant Island (1)
{ Zavodovski, South Sandwich Gp. (0)
Islands of the South Atlantic Ocean
{ Gough Island (5)
{ Tristan da Cunha (2½)
{ Nightingale (1)
{ Middle (1)
{ Stoltenhoff (0)
{ Inaccessible (1)
Islands of the Mid-Atlantic
{ St. Paul’s Rocks (½)
{ Saõ Miguel Açores, St. Vincent
{ (Cape Verdes) (3)
{ Ascension (3)
{ St. Helena (1)
(The numbers in brackets refer to the days spent ashore.)

ISLANDS OF THE SOUTHERN OCEAN

South Georgia.—Lat. 54° S. Long. 37° W.

Topography

This island is about 116 miles long by 20 miles wide, with the longer axis lying in a general N.W. and S.E. direction. It has the appearance of an upland dissected by cirque recession and enlargement. The highest peak, Mount Paget, which is an isolated remnant of the upland, is about 8,000 feet high.

Termination Of Ross Glacier | South Georgia | 8th May, 1922 | Shackleton-Rowett Expedition

The average peaks in the comb ridges are about 2,000 feet, and the average level of the interior would be placed by the writer as about 600 feet above sea level. The glacial valleys run in general across the longer axis and are separated from each other by comb ridges. The majority of the glaciers show signs of withdrawal. At the N.W. end of the island many of the valleys are free of ice altogether.

One interesting investigation was carried out at Royal Bay, where the Ross Glacier comes down to the sea. The position of the foot of the glacier relative to the shore was first measured by the Gauss Expedition of 1882, then again by Nordenskjold in 1902, and then by the members of the Quest in 1922.

These measurements show this interesting fact—that there was an advance of the foot of over 4,000 feet during the period 1882 to 1902, and that now it is back in the position of 1882. It is suggested that this does not indicate any general advance or withdrawal, but rather that the glacier, which is operating, to use an hydraulic term, under a high head is being forced out to sea where the foot is afloat. It will continue to advance until the effect of the rollers on the floating mass of ice overcomes the tensile strength of the ice and it breaks away. If we assume that twenty (20) years represent this period (it may be a multiple of a smaller period), then this gives an advance per year of about two hundred and twenty (220) feet.

Geology

From Cooper Bay to Bird Island the rocks seen by the writer were of sedimentary origin. They are of the nature of grits, tuffs and phyllites. To the east of Cooper Bay the rocks are igneous. The basement is of a basic nature, with flows, at least two in number, over it. Back from Cooper Bay, and just east of the contact with the sediments, there is a small stock of a more acid rock, which has been called a syenite.

A provisional table is here drawn up to show the relative age relations, with the more recent at the top:

AT LARSEN HARBOUR
Epidosite }
Spilite } Doleritic dykes cutting these.
Gabbro }
NORTH-WEST OF DRYGALSKI FJORD
Quartz diorite stock Complex system of dykes.
Gabbro
Booby With Chick On St. Paul’s Rocks | Photo: Wilkins
A Booby Chick On St. Paul’s Rocks | Photo: Wilkins
Types Of Fish Caught In The Lagoon At St. Paul’s Rocks | Photo: Wilkins
White-capped Noddies At St. Paul’s Rocks | Photo: Wilkins

Tectonic Movements

The sedimentary rocks have been subject to considerable folding and faulting. From the direction of the folds and the general trend of the line of schistosity it would appear that the pressure had come from the S.S.W. or N.N.E.

Age

A few fossils of a very indefinite character were obtained, and are now being worked out.[16] Provisionally it may be said that one, a fossil plant probably of the Araucaria type, points to an age not older than lower carboniferous.

Elephant Island.—Lat. 61° S. Long. 55° W.

This is one of the easterly islands in the Powell group of the South Shetlands, and was only landed on at two points, Lookout Harbour and Minstrel Bay.

Topography

The features of Elephant Island probably are similar to what those of South Georgia were before the intense glacial erosion sculptured the island as already described.

Powell Group | South Shetlands

It is a plateau feet at the rim, but rising gently towards the interior. It appeared to be covered by an ice sheet, and the same may be said of Clarence Island, which lies a few miles to the eastward; only in the latter case there was a definite cliff of ice visible above the rock face.

The glaciers were more of the hanging than of the valley type. Especially was this so on the west coast.

Geology

The rock specimens collected and the little mapping which was done indicate that the island is composed mostly of sedimentary rocks which have been much metamorphosed. Phyllites predominated, but various schists, slates and banded limestones were also seen.

Zavodovski.—Lat. 56° S. Long. 27° W.

This island, the most northerly in the South Sandwich group, was not landed on by the members of the Quest, and the following observations from the ship must be considered only probable and in no way certain.

The island is of volcanic origin, rising as a cone from the sea. The upper levels were not seen by us, but the height of the summit is given by Bellingshausen as 1,200 feet. The cliff rises vertically from the sea about 40 feet, and then there is a long, gentle slope gradually getting steeper.

The lava flows seen on the cliff face appeared to consist of a compact columnar basalt at the base. Above there was a line of red cinder, and above this again what looked to be rough pahoehoe lava. A number of clefts and vents were seen on the face of the cliff, and from these there issued bluish fumes.

Soundings with the Kelvin were taken every half-mile or so, and the material collected corresponds with the basalts and cinder mentioned.

It was unfortunate that we were unable to visit the other islands in this group, for with the exception of the scanty reports of Bellingshausen, C. A. Larsen and a German expedition, the geology and natural history are practically unknown, and the existing charts are not by any means complete.

PETROLOGICAL REPORT, by W. Campbell Smith, M.C., M.A., British Museum of Natural History.

Rock fragments washed from material dredged at 19 fathoms off Zavodovski, South Sandwich group, 20/1/22.

The sample consisted of a few grammes of rounded black pellets varying in diameter from 1 to 5 mm. They consisted of the following:

Ten dense black glassy basalts. All appear free of olivine. Some are crowded with minute laths of plagioclase; others contain fewer minute laths but show a few small phenocrysts of plagioclase, or of augite, or both.

Four dense dark-brown glassy olivine-basalts, some containing many crystals of plagioclase, and a few crystals of olivine and augite. The glass is crowded densely with magnetite and sometimes with other undetermined microliths.

Four rather paler basalts with holocrystalline-porphyritic texture. These contain very small phenocrysts of plagioclase and sometimes of augite, in a ground mass of very minute laths of felspar and grains of augite and magnetite. The texture of the ground mass is intergranular. One of the specimens contained no augite phenocrysts, but rather numerous microphenocrysts of magnetite.

Two small fragments of pale basalt-glass, deep olive-buff in colour. Microliths are absent in one specimen, but they are abundant in the other and consist of small laths of plagioclase, and minute prisms of augite and a few crystals of what is probably olivine. The felspar laths gave extinction angles of 15°, but only a very few measurements could be made. This material resembles the pale patches of glass in the palagonite tuffs of Sicily and of Kerguelen Land,[17] and a somewhat similar though darker coloured rock has been described from Schwartzenfels Hesse as vitrophyric basalt, and has been elegantly figured by Berwerth.[18]

ISLANDS OF THE SOUTH ATLANTIC OCEAN

Gough Island.—Lat. 40° S. Long. 10° W.

Gough Island lies roughly 200 miles south of the Tristan da Cunha group. It is 8 miles long by 3 miles wide.

Topography

The island forms a monoclinal block with dip slopes to the west and escarpments to the east. The highest point on the long ridge which runs down the longer axis of the island is about 2,915 feet above sea level.

The west side of the ridge goes down in a long slope to the cliffs bordering the sea.

The escarpments on the east side are cut by three or four glens. The largest one, about half-way down the coast, gives access to the interior.

The most striking feature, looking up the glen, is the great stock of an acid intrusive rock, which rises to 2,270 feet. It can best be described in the words of Scott:

Shooting abruptly from the dell

Its thunder splintered pinnacle.

Geology

The island is the result of a series of fissure flows of a basaltic and trachytic nature. These flows have been intruded by the  stock just mentioned above, and many fissures were opened by it. These have subsequently been filled by dykes. The rock forming the dykes is very hard, with the result that they are now a very prominent feature, and stand up in some cases about 50 feet above the surrounding country. This is due, of course, to differential weathering.

It is probable that the east coast represents a fault plane, but as the erosion has been great, direct evidence is wanting. Apart from this fault no faulting nor folding was observed.

Gentoo Penguin With Two Chicks | Photo: Wilkins
Nesting Ground Of The Mollymauk | Photo: Wilkins
Giant Petrel At Nest | Photo: Wilkins

Tristan da Cunha.—Lat. 37° S. Long. 12° W.

Topography

Tristan is an island octagonal in plan, about 8 miles across. It rises as a prism for about 2,000 feet, and then tapers off as a cone to about 6,400 feet above sea level. The crater is now filled with water, and at that level is about 200 feet across. The rainfall on the upper slopes is very great, and they are deeply eroded. At the foot of the cliff, on the northern shore, there is a gently sloping lava plain, upon which the settlement is situated. In extent it is about 3½ miles long by half a mile wide. About midway between the extremities there are a few small craters rising above the plain. The plain is grass clothed, and the upper slopes are covered in moss, bracken and scrub trees. This vegetation continues up to about 4,000 feet, above which point the rocks are bare.

Geology

The island consists of a great series of lava flows which have poured from the volcano, and are of the nature of scoriæ, cinder, trachyte and basalt in succeeding and alternating layers. As is so common on these volcanic islands, the lower lava is generally a hard, compact basalt showing rough columnar structure.

Only one section was observed, which is placed below, but there is good reason to believe that to the west, in the neighbourhood of Swain Bay, more complex conditions exist, as many samples of bombs of a rock carrying large crystals of felspar and hornblende and other coarse grained rocks were given to the writer by some of the islanders, who stated that they came from this locality.

Preliminary note by W. Campbell Smith, M.C., M.A., on the samples given by islanders at Tristan da Cunha and reported to have come from the neighbourhood of Swain Bay. The specimens can be grouped in four types:

  1. Rocks with felspar almost nil. Probably consist mainly hornblende and pyroxene, with perhaps some olivine, apatite and magnetite.
  2. Rocks with a little felspar and characterized by large poikilitic plates of hornblende. These contain abundant pyroxene, and some olivine, apatite and magnetite.
  3. Rocks with long, thin blades of hornblende in a fine-grained matrix of labradorite, and with some patches of black “glass” and abundant minute prisms of apatite. In hand specimens these look like dyke-rocks, but I think the texture and the patches of magnetite show that they are segregations.
  4. Coarse-grained rocks with perhaps more felspar than hornblende. Hornblende in large crystals in a matrix of labradorite. The texture is coarser than in the preceding type. Felspars reach 2 or 3 mm. in diameter. The hornblende includes some small crystals of yellow pyroxene. Apatite and magnetite are given abundant.

All four types appear to be closely inter-related. They contain the same minerals in varying proportions and probably grade one into the other.

The obsidian and the pieces of red glass are basalt glass, and are probably similar to the specimen described by Renard in the Report on the Challenger Collection, p. 82. He states that the inhabitants use the rock for striking fire.

OBSERVED SECTION FROM THE PEAK TO HERALD POINT

Elevations. Rock provisionally named. Remarks.
FEET
6,400 Scoriæ and vesicular basalt. Forming summit.
6,200-5,700 Loose scoriæ and bombs. Crater cone.
5,700-5,500 Basalt.
5,000-4,550 Trachy-basalt.
4,400 Vesicular basalt.
4,300 Trachytic agglomerate.
4,250 Compact basalt.
4,150 Red scoriæ.
3,950 Basalt.
3,750 Scoriæ.
3,600 Scoriæ and basalt. A contact.
3,520 Basalt and scoriæ. A contact.
3,420 Scoriæ and basalt. A contact.
3,220 Grey basalt.
(Break in the observations).
1,200 Basalt and scoriæ. A contact.
(Break in the observations).
225 Basalt. This rock is used for building the dwellings by the inhabitants.
223 Cinder.
222 Scoriæ.
220 Tuff.
216 Agglomerate.
To sea level. Compact basalt. Rough columnar structure.

A number of vapour vents were observed at different points.

It is apparent that the small craters mentioned above as existing on the settlement plain sprang up after the main period of eruption when the island was built.

To the west and about 22 miles from Tristan there are the four islands—Nightingale, Middle, Stoltenhoff and Inaccessible.

Nightingale

Topography

This island, which is the most southerly of the group, is rectangular in plan, one mile by three-quarters. High cliffs bound the south, east and west sides. The northern slopes descend gradually to the sea, where they terminate in cliffs about 30 feet high.

The highest point is on the east side of the island, and is about 1,000 feet above sea level. It is connected by a low featured col  to the high land to the south-west. To the west, that is, towards the interior of the island, there is a depressed area which now has a small pond in it. It is probable that this was once the crater from which the lavas issued.

Geology
One day only was available for work on this island, and orders were that the supposed guano deposits which were reported at the north side were to be examined. These deposits are of no economic value, and an analysis is here appended.

Certificate of Analysis. | Ogston and Moore, Analytical Chemists | 89 Aldgate, London | July 28, 1922.

Guano from Nightingale Island.

Moisture 72.12
Organic matter and ammonia salts 24.70
Phosphoric acid nil
Lime nil
Magnesia, alkalies, etc. 1.60
Silicious matter 1.58
100.00

Guano from Cave on Middle Island.

Moisture 17.00
Organic matter and ammonia salts 15.15
Phosphoric acid 3.85
Lime 5.10
Magnesia, alkalies, etc. 10.20
Silicious matter 48.70
100.00

The rocks, however, appeared to be in general of a trachytic nature.

Middle Island

Topography

Middle Island lies less than half a mile to the north of Nightingale. It is in plan about a quarter of a mile square, and rises to a height of about 200 feet. It is flat-topped, with minor depressions.

Geology

There have been questions asked as to the origin of Middle Island, and to the writer, who had this in mind when visiting the island, the following were the reasons for its existence.

The trachytic flows from Nightingale probably extended at one time about a mile farther to the north than the present northern shore of Nightingale. This is evidenced by the trachytic agglomerate and trachyte seen on Middle. Following this there was an effusion of a hard, compact lava from a neck which exists on the latter island. The border of the neck is marked by a breccia. The dykes emanating from this lava are not seen on Nightingale, but some of the rocks which infest the channel between the islands are probably their eroded remains. The action of the sea on the mass of altered trachyte between Middle and Nightingale Islands has in the course of time cut a channel through.

Stoltenhoff

It is not possible to land on this island, as it rises sheer from the sea to about 200 feet. It is flat-topped, and in area about 500 yards by 150 yards. The rock of which it is composed appears to be of a trachytic nature, and may be the northern limit of the flow’s from Nightingale, which have already been mentioned; it may, however, be a centre of activity, such as is described as existing on Middle Island.

Inaccessible Island

Topography

Eleven miles to the N.N.W. from Stoltenhoff is this island, which is the most northerly one of the group. In plan it is pear-shaped, being about 3 miles by 2½.

In its general features it is a basin, being a great caldera, the south-east side of which has been blown out. A cone rises to about 1,500 feet towards the north-east of the depressed central area. The interior is broken country clothed in verdure, and on account of the high rim, which affords protection from the winds, would be suitable for human habitation. A stream winds through the interior, finally falling in a beautiful cascade to the beach at the north-east shore, where a landing is easily made if the wind is not from the north.

 

Geology

The central cone is a mass of scoriæ, and the section from here to the sea near the waterfall shows that there have been successive flows of basalt and trachyte. The high cliffs to the west of the landing are cut by a series of parallel dykes, which are an outstanding feature.

ISLANDS OF THE MID-ATLANTIC OCEAN

The St. Paul’s Rocks

These lie just north of the equator, almost midway between Africa and Brazil. These rocks are almost unique in occurrence, for, as Charles Darwin remarks in his journal, “Its mineralogical constitution is not simple…. It is a remarkable fact that all the many small islands, lying far from any continent, with the exception of the Seychelles and this little point of rock, are composed either of coral or erupted matter.”The St. Paul’s Rocks are a group of eight or nine small rocky islands, the largest of which is only about 350 feet long by 150 feet wide. This island and the most northerly were the only ones where a landing was effected.

The whole of the southerly portion of the main island is composed of a highly weathered rock which has thin veinlets of serpentine cutting through it. Running in a north and south direction, and in places dragged and folded and cutting this formation, there is a dyke, which stands up prominently from the main country rock. About 30 yards to the east the rock is cut by a series of irregular interlacing narrow dykes having the appearance of old concrete. The ground mass is hard and to the eye amorphous. It contains rounded pebbles and possibly shell remains.

Towards the centre of the main island the rock formation changes abruptly to a compact glassy green rock, probably a peridotite. It has developed a jointing, and but for the conglomerate forms the remainder of the island and possibly the other islands as well, because the country rock on the north island is of a similar nature.

Along the inside of the central basin at two points there occurs a conglomerate—pebbles ranging from 3 inches in diameter to a fraction of an inch cemented in a matrix.

Towards the north end there is a fault which crosses the island in a N.W. and S.E. direction, and parallel to which there is a dark, rusty dyke.

In two or three places on the main island, one of which is near this fault, there are small pot holes. There was a rounded boulder in each, and probably, as the sea comes swirling in at high tide, a rotary motion is given to the boulder and the pot hole develops.

The general formation of the islands might be described as a stock of glassy peridotite which has risen from the bed of the ocean and of which only the highest points are now visible.

Saõ Miguel Açores, St. Vincent (Cape Verde), Ascension and St. Helena

The above islands were called at and examined, but as the geology has already been described by others who had more time at their disposal, no new light was thrown on them. The visits, however, were valuable in that they will enable the writer to compare the conditions existing at these places with the seldom visited islands already above described.

DEEP-SEA SOUNDINGS

In collaboration with the hydrographer, material from the sea floor was obtained by soundings in various localities. This material is being examined microscopically, and its physical properties are being determined (specific gravity, gradation of sizes, radioactivity, etc.).

GENERAL OBSERVATIONS

The general reader is reminded that the geological observations recorded here are in no way complete. Much detailed work is necessary on these various islands before the full record can be written. Nature has laid open the story of her history to the careful investigator, but from the casual one she withholds the deeper meaning.

ACKNOWLEDGMENTS

The writer wishes in conclusion to thank the following for their hearty co-operation, which made the above results possible:

Capt. G. H. Wilkins, M.C., F.R.G.S.
Major C. R. Carr, D.F.C.
Messrs. Dell, Argles and Marr.

The work at South Georgia would have been impossible but for the kind assistance of the managers of the whaling companies:

The De Pesca Company, of Buenos Aires
The Southern Whaling Company (Lever Bros.)
The Tönsberg Company, of Norway
The Westfahl Company, of Norway
The Salvesen Company, of Leith, Scotland
The excellent surveying instruments which were so kindly lent by Messrs. Troughton and Simms proved invaluable under all conditions.

Thanks are specially due to Mr. John Quiller Rowett, LL.D., without whose generous support the expedition would have been impossible.

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