| Sea Bear Bay. | Indian. | Holme's Bird Island. | Ascension Island. | Possession Island. | |
| Water | 30·82 | 23·62 | 25·00 | 15·97 | 10·92 |
| Organic matter and ammoniacal salts | 31·78 | 60·05 | 32·10 | 23·15 | 15·42 |
| Phosphates | 24·33 | 7·18 | 27·36 | 32·54 | 46·41 |
| Sulphate of lime | 3·84 | ... | ... | ... | 7·46 |
| Carbonate of lime | 0·58 | 2·79 | ... | ... | ... |
| Alkaline salts | 7·38 | 5·58 | 8·82 | 15·92 | 6·15 |
| Sand | 1·27 | 0·78 | 6·72 | 12·42 | 13·64 |
| 100·00 | 100·00 | 100·00 | 100·00 | 100·00 | |
| Ammonia | 10·45 | 10·27 | 7·75 | 6·06 | 1·34 |
| Phosphoric acid in alkaline salts | ... | ... | ... | 1·82 | ... |
| Algoa Bay. | New Island. | Bird's Island. | Leone Island. | |
| Water | 30·55 | 28·78 | 16·52 | 23·65 |
| Organic matter and ammoniacal salts | 6·85 | 13·78 | 14·84 | 4·27 |
| Phosphates | 21·24 | 22·46 | 25·21 | 13·58 |
| Sulphate of lime | 36·42 | ... | 40·47 | 29·95 |
| Carbonate of lime | ... | 13·78 | ... | ... |
| Alkaline salts | 3·32 | 12·62 | 1·16 | 5·40 |
| Sand | 1·62 | 11·58 | 1·80 | 23·15 |
| 100·00 | 100·00 | 100·00 | 100·00 | |
| Ammonia | 0·54 | 0·84 | 1·26 | 0·67 |
| Phosphoric acid in alkaline salts | ... | ... | ... | ... |
On examining the tables given above, it is obvious that guanos may be divided into two classes, the one characterized by the abundance of ammonia, the other by that of phosphates; and which, for convenience sake, may be called ammoniacal and phosphatic guanos. Peruvian and Angamos are characteristic of the former, and Saldanha Bay and Bolivian of the latter class. The value of these two classes of guano differs materially, and they are also applicable under different circumstances, but to these points reference will afterwards be made.
Very special precautions are necessary on the part of the farmer in order to insure his obtaining a guano which is not adulterated, and of good quality if genuine. In the case of Peruvian guano, which is tolerably uniform in its qualities, it is possible to form some opinion by careful examination, and the following points ought to be attended to:
1st, The guano should be light coloured. If it is dark, the chances are that it has been damaged by water.
2d, It should be dry, and when a handful is well squeezed together it should cohere very slightly.
3d, It should not have too powerful an ammoniacal odour.
4th, It should contain lumps, which, when broken, appear of a paler colour than the powdery part of the sample.
5th, When rubbed between the fingers it should not be gritty.