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Parr IL § vi] FRAGMENTAL ROCKS—ORGANIC. 169. 
carbonate has been effected by a process of chemical pseudomor- 
phism either after or during the formation of the limestone. The 
vertical ramifying masses of flint in chalk show that the calcareous 
‘ooze had to some extent accumulated before the segregation of these 
masses.’ 
(3.) Phosphatie. 
A few invertebrata contain phosphate of lime. Among these 
may be mentioned the brachiopods Lingula and Orbicula,? also 
Conularia, Serpulites, and probably some crustacea. The shell of the 
recent Lingula ovalis was found by Hunt to contain, after calcination, 
61 per cent. of fixed residue, which consisted of 85°70 per cent. of 
phosphate of lime; 11°75 carbonate of lime, and 2°80 magnesia. 
The bones of vertebrate animals likewise contain about 60 per cent. 
of phosphate of lime, while their excrement sometimes abounds in 
the same substance. Hence deposits rich in phosphate of lime have 
resulted from the accumulation of animal remains from Silurian 
times up to the present day. These certainly are far inferior in 
extent and importance to the calcareous, and even to the siliceous, 
formations, yet they are often of singular geological interest. The 
following examples may serve as illustrations. 
Guano.—A deposit consisting mainly of the droppings of sea-fowl, 
formed on islands in rainless tracts off the western coasts of South 
America and of Africa. It is a brown, light, powdery substance with 
a peculiar ammoniacal odour. Analyses of American guano give 
—combustible organic matter and acids, 11°3 ; ammonia (carbonate, 
urate, &c.), 31°77; fixed alkaline salts, sulphates, phosphates, 
chlorides, &c., 8-1; phosphates of lime and magnesia, 22°5; oxalate 
of lime, 2°6 ; sand and earthy matter, 1:6; water, 22°2. This remark- 
able formation is highly valuable as a source of artificial manures. 
(Book ITI. Part II. Section ii1.) ee 
Bone-Breccia.—A deposit consisting largely of fragmentary 
bones of living or extinct mammalia, found sometimes under stalag- 
mite on the floors of limestone caverns more or less mixed with 
earth, sand, or lime. In some older geological formations, bone- 
beds occur, formed largely of the remains of reptiles or fishes, as the 
“ Lias bone-bed,” and the “ Ludlow bone-bed.” , 
Coprolitic nodules and beds*—are formed of the accumulated 
excrement of vertebrated animals. Among the Carboniferous shales 
of the basin of the Firth of Forth, coprolitic nodules are abundant, 
together with the bones and scales of the larger ganoid fishes which 
yoided them; abundance of broken scales and bones of the smaller 
1 On formation of chalk flints, see Wallich, Q. J. Geol. Soc. xxxvi. p. 68. Sollas, 
Ann. Mag. Nat. Hist. 1880. Hull and Hardman on Chert, Trans. Roy. Dub. Soc., new 
series, vol. i. p. 71, 1878. 
? Sterry Hunt, Amer. Journ. Soc. xvii. (1854), p. 236. Logan’s Geology of Canada, 
1863, p. 461. 
3 On the origin of phosphatic nodules and beds, see Gruner, Bull. Soc. Géol. France, 
ExXvViii. (2nd ser.) p. 62. Martin, op. et. iii. 3rd sec. p. 273. 
