374 



REPORT OF NATIONAL MUSEUM, 1899. 



islands of Malta, Gozo, and Comino, of the Maltese group in the Med- 

 iterranean Sea. The bed containing- the nodules is in what is known 

 as the Globigerina limestone, which underlies an upper coralline lime- 

 stone, greensands, and blue clays, and overlies the lower coralline 

 limestone. Upper and lower beds all carry phosphoric acid in small 

 amounts. There are four seams of nodules, the first varying in differ- 

 ent localities from 9 to 15 inches in thickness. The second is more 

 constant in character, averaging some 2 feet in thickness and consist- 

 ing of an aggregate of irregularly shaped nodules, intermixed with 

 which are considerable quantities of the phosphatized remains of mol- 

 lusks, corallines, echinoderms, crustaceans, sharks, whales, etc., the 

 whole being firmly bound together by an interstitial cement, composed 

 of foraminiferal and other calcareous matter similar to that of which 

 the overlying beds are made up. The third seam is the poorest of the 

 lot and consists of two or more thin layers of nodules, none of which 

 exceeds 3 inches in thickness. Between this and the fourth and lowest 

 seam, which is the most important of all, is a bed of rock some 50 to 

 80 feet in thickness. The seam averages some 3i feet in thickness. 

 The nodules are of a dark-chocolate color embedded in a calcareous 

 matrix, from which they are freed by calcination. The composition of 

 I, the nodules, and II, the average composition of nodules and inter- 

 stitial cement, is given below, from analyses by Drs. Murray and 

 Blake: 



Constituents. 



Sulphate of lime 



Carbonate of lime 



Phosphate of lime 



Alumina { AUOs) 



Oxide of iron (FeoOs) 

 Residue 



Total . 



2.26 



47.14 



38.34 



5.98 



Trace. 



6.08 



99.80 



1.97 

 61.12 

 31.66 

 10.59 

 a 3. 83 

 6 0.87 



100.00 



a Silica. 



b Moisture. 



Guano, soluble and leached. — The largest and best-known de- 

 posits of unleached guanos are found on the mainland and small 

 islands off' the coasts of Peru and Bolivia, where abundant animal life 

 and lack of rainfall have contributed to their formation and pre- 

 servation. These deposits are described as consisting mainly of the 

 evacuations of sea fowl and marine animals, such as flamingoes, divers, 

 penguins, and sea lions. Mixed with these deposits are naturally more 

 or less bone and animal matter furnished by the dead bodies of both 

 birds and mammals. The deposits vary indefinitely in extent and 

 thickness, but have attained in places a depth of upward of 100 feet. 

 As a rule they are more compact beneath than at the surface, but 



