| Moisture | 72.12 |
| Organic matter and ammonia salts | 24.70 |
| Phosphoric acid | nil |
| Lime | nil |
| Magnesia, alkalies, etc. | 1.60 |
| Silicious matter | 1.58 |
| 100.00 |
Guano from Cave on Middle Island.
| Moisture | 17.00 |
| Organic matter and ammonia salts | 15.15 |
| Phosphoric acid | 3.85 |
| Lime | 5.10 |
| Magnesia, alkalies, etc. | 10.20 |
| Silicious matter | 48.70 |
| 100.00 |
The rocks, however, appeared to be in general of a trachytic nature.
Middle Island
Topography
Middle Island lies less than half a mile to the north of Nightingale. It is in plan about a quarter of a mile square, and rises to a height of about 200 feet. It is flat-topped, with minor depressions.
Geology
There have been questions asked as to the origin of Middle Island, and to the writer, who had this in mind when visiting the island, the following were the reasons for its existence.