pless offspring; and, in the third place, it must be so situated that
the young can reach the water in safety. We will examine these
conditions one by one.

The proximity to the food-supply is a consideration of some importance.
The life of the Guillemot during the winter is a strenuous one; we know
that large numbers succumb in stormy weather, and we can infer that
slight constitutional defects might make all the difference between
failure and success; and, therefore, the less severely the constitution
of the parent is taxed during reproduction, and the more securely the
constitution of the offspring is built up, the greater prospect will
both have of resisting the hardships of the winter successfully. Much,
then, will depend upon the distance the parents have to travel in order
to obtain food. The farther the breeding station is removed from the
feeding ground the greater the physical strain which will be imposed
upon the birds, and the greater the chance will there be of the
offspring being improperly nourished. Now the food consists of small
fish, largely of sand-eels, which are secured in deep water, and the
abundance of which varies, possibly according to the nature of the
currents. Hence cliffs which are situated away from the water, or from
which the water recedes at low tide, or which are surrounded by an area
of shallow water, and are thus not in proximity to the feeding ground,
even though they may fulfil the second and third condition, will not
answer the requirements of a breeding station.

Of no less importance is the type of rock-formation. Not every formation
affords the necessary ledges upon which the egg can be deposited with
safety--the face of the cliff may be too smooth, or too jagged, or the
shelves may run at too acute an angle. Many of the large assemblages of
Guillemots in the British Islands are found where the rock is quartzite,
mica-schist, limestone, or chalk. The reason of this is that such rocks
are weathered along the planes of stratification, of jointing, of
cleavage, or of foliation--the strata being probably of unequal
durability--with the result that innumerable shelves, ledges, and
caverns, which are taken advantage of by the birds, form a network over
the face of the cliff. But only those ledges can be made use of which
are placed at a considerable height above the water, because, when the
cliff faces the open sea, the lower ones are liable to be washed in
stormy weather by the inc