1904 - 5.1 Graptolite-bearing Bocks of the South Orkneys. 463 
On the Graptolite-bearing Rocks of the South Orkneys. 
By J. H. Harvey Pirie, B.Sc., M.B., Ch.B. Communi- 
cated by Dr Horne, F.R.S. With a Note by Dr Peach on 
Specimens from the South Orkneys. 
(MS. received February 7, 1905. Read February 20, 1905.) 
The South Orkneys are a small group of islands situated in the 
Southern Ocean, in about 62° S. lat. and 45° W. long., roughly 
800 miles S.E. of Cape Horn. A single landing was made from 
the “ Scotia ” on Saddle Island, a small island on the north side 
of the group, and another on Coronation Island, the largest and 
most westerly. With these two exceptions all the rock specimens 
were obtained on Laurie Island, the most easterly of the group. 
The rock got on Coronation Island is a coarse conglomerate, in 
which the bedding is well marked, the individual beds averaging 
about 2 feet in thickness, and dipping at about 30° in a north- 
easterly direction. The rock is composed of a mixture of rounded 
waterworn pebbles and of angular fragments of dark-coloured shale 
and mica-schist. Whether this rock belongs to the same series as 
the Laurie Island beds or not I do not know, but the strike is 
approximately the same. 
Saddle Island is composed of a massive greenish grey wacke, very 
similar to the Laurie Island rocks. The typical rock of Laurie 
Island is a fine-grained greywacke of a blue-grey or greenish-grey 
colour. To the naked eye it appears almost homogeneous : the 
only constituents that can be recognised are some minute rounded 
quartz grains, small black shaly particles, and a few specks of 
pyrites. Thin quartz and calcite veins traverse the rock irregu- 
larly. A microscopic section shows that the derived constituents 
consist of angular and sub-angular grains, with a mean diameter 
of about 0’2 mm. The great majority of these are quartz, originally 
of plutonic origin ; there are also a goodly number of small 
crystals of plagioclase, wonderfully fresh, some grains of both 
sphene and zircon, and a few minute flakes of biotite. The 
