dred miles distant from any continent, appear to have been raised from the bed of the ocean by volcanic agency, and not in any part exceeding seventy feet above its surface, present the form of an oblong crater, the longer axis lying in a N.E. and S.W. direction. Mr. Darwin, however, considers them not to be of igneous origin, and, in this particular, unlike all the other detached islands of the Atlantic.
The following geological remarks upon them are by Mr. McCormick, surgeon of the Erebus, who attended to that branch of natural knowledge:—
"Situated nearly on the equator, in latitude 0° 56′ N., and longitude 29° 20′ W.; they consist of a group of rocks, altogether scarcely exceeding half a mile in circumference. The four largest form a kind of bay on the N. W. side, in which there is a considerable swell, from the surf breaking heavily through the three channels by which these rocks are separated from each other. The highest rock is on the N.E. side of the bay, rather sharply peaked, seventy feet above the level of the sea. The next in height, and the most remarkable, from its uniform white colour, is sixty-one feet, and situated on the S.W. or opposite side. This rock is composed of a very hard kind of hornstone, readily affording sparks under a blow of the hammer, and coated over with a thin layer of calcareous matter, evidently produced from the excrement of the numerous birds which have selected this spot as a breeding-place.
