4 T. V. HODGSON. 
water never came within five miles of the ‘ Discovery,’ so that in the following season 
its gradual approach was watched with more than ordinary interest, not to say 
anxiety. On January 4th, 1904, when the relief ships arrived there were at least 
eighteen miles of ice still to go; some fourteen miles went out in about six weeks, 
but on February 14th the necessary conditions obtained, and four miles of fast 
ice broke up and started northwards in about as many hours. At the time it 
was practically a dead calm, so that the wind had no influence. When we 
passed Winter Harbour for the last time, on February 18th,’ the last masses of 
ice were floating out, a phenomenon which had occurred one day earlier two years 
previously. 
The foregoing is the briefest possible account of the ice conditions prevailing 
in McMurdo Sound, and is not without biological interest, as by it the Sound may 
be divided into three areas. 
The first, or Northern area, extends from Cape Bird to the so-called “ glacier 
toneue,” and includes the Dellbridge Islands. This is on the eastern side of the 
Sound. A line drawn from the “Glacier Snout” to the southern boundary of New 
Harbour forms the southern limit of this area. Open water occurs in this area for 
at least four months of the year as a general rule; in the more northern part of the 
area, beyond Cape Royds, the period of open water is probably much longer. This 
is incontestably proved by the Penguin rookery at Cape Royds and the large 
breeding place for the Skua at Skuary Point, neither of these species going far from 
water except in occasional wanderings. The Penguin requires open water and a 
convenient landing place, both of which were obtainable at Cape Royds; the Skua 
is less dependent on either, but seeks for the former. Our presence brought immense 
numbers to Hut Point, but only a few stragelers bred there; they bred in very 
large numbers on the numerous islets on both sides the Sound, where the open water 
was within easy reach. 
The second, or Central area, includes the rest of the Sound south of the Glacier 
Tongue and New Harbour, which is periodically open to navigation, rarely exceeding 
a couple of months at this point, a good deal less than that south of Cape Armitage. 
A small area of open water occurred under Hut Point during the summer, caused 
mainly by the ice-movements in the vicinity. A large lake also appeared off 
Cape Armitage, over a shoal, and was fully half a square mile in area. The 
explanation of this phenomenon ultimately arrived at was that the shoal brought 
the deeper and warmer waters of the Sound to the surface as the current swept 
past the Cape, and so melted the ice through. This oceurred in January 1902 and 
1903, and a little later in 1904. It had just frozen over when we arrived in 1902. 
The third, or Southern area, is much the largest, and includes the whole of that 
part occupied by the permanent or barrier ice. As the ice is covered as soon as it is 
formed by a thick deposit of salt crystals and very shortly afterwards by snow, it 
forms an opaque covering over the sea bottom through which no light can penetrate, 
