When we came on deck the next morning, we were passing along the coast of Ayrshire, within sight of Ailsa Crag, a fine rock, which stands out of the sea to a great height.  It is a mass of columnar trap of a grey colour.  We steered so as to pass it on our starboard side.  We had come in sight of the southern face, where we could distinguish a square tower, perched on a terrace, about two hundred feet above the sea.  The ascent to the summit must be no easy matter.  As we sailed on, we came off the north-west side, which is almost perpendicular, and composed of successive tiers of enormous columns.  Here we made out a cave, above which was a grassy declivity sloping upwards towards the summit.  Though it is at the very mouth of the Clyde, its great height causes it to be seen at a distance, preventing it being dangerous to vessels bound to Glasgow.  Any person inclined to solitude might take up his abode there, and live without leaving it, as it is inhabited by numerous flocks of sea-fowl, with goats and rabbits; while nettles, and a variety of hardy plants, grow in the interstices of the rocks.  I asked Dick if he would like to remain there, saying that I would get papa to put him on shore, if he wished it; but he declined the offer, preferring rather to go back to school at the end of the holidays.