170 GEOGNOSY. [Boor IL. — 
ganoids can usually be observed in the coprolites. Among the 
Lower Silurian rocks of Canada, numerous phosphatie nodules, 
supposed to be of coprolitic origin, occur.’ Associated with the 
Bala limestone in the Lower Silurian series of North Wales is a 
band composed of concretions cemented in a black graphitic, slightly 
phosphatic, matrix, and contaiing usually 64 per cent. of phosphate 
of lime (phosphorite).? The tests of the trilobites and other organ- 
isms among the Cambrian rocks of Wales also contain phosphate of 
lime, sometimes to the extent of 20 per cent.* The phosphatic beds 
of the Cambridgeshire Cretaceous rocks are now largely worked as 
a source of artificial manure. 
(4.) Carbonaceous- 
The formations here included have almost always resulted from 
the decay and entombment of vegetation on the spot where it grew, 
sometimes by the drifting of the plants to a distance and_ their 
consolidation there. (See Book III. Part II. Section i1., Lire.) 
In the latter case, they may be mingled with inorganic sediment, 
so as to pass into carbonaceous shale. 
Peat.— Vegetable matter, more or less decomposed and chemically 
altered, found throughout temperate climates in boggy places where 
marshy plants grow and decay. It varies from a pale yellow or 
brown fibrous substance, like turf or compressed hay, in which the 
plant-remains are abundant and conspicuous, to a compact dark- 
brown or black material, resembling black clay when wet, and some 
varieties of lignite when dried. The nature and proportions of the 
constituent elements of peat, after being dried at 100° C., are 
illustrated by the analysis of an Irish example which gave—carbon, 
60:48; hydrogen, 6:10; oxygen, 32°55 ; nitrogen, 0°88; while the 
ash was 3°30. 
There is always a large proportion of water which cannot be 
driven off even by drying the peat. In the manufacture of com- 
pressed peat for fuel this constituent, which of course lessens 
the value of the peat as compared with an equal weight of coal, is 
driven off to a great extent by chopping the peat into fine pieces, 
and thereby exposing a large surface to evaporation. The ash - 
varies in amount from less than 1:00 to more than 65 per cent.,. — 
and consists of sand, clay, ferric oxide, sulphuric acid, and minute | 
proportions of lime, soda, potash, and magnesia.* 
Lignite (Brown coal).—Compact or earthy compressed and 
chemically altered vegetable matter, often retaining a lamellar or 
lioneous texture, with stems showing woody fibre crossing each other in 

1 Geology of Canada, p. 461. id 
2). ©. Davies. Q: J. Geol. Soc. Xxxi. p. 357. . * Hicks, op. cit. p. 368, 
4 See Senft’s Humus- Marsch- Torf- und Limonit-bildungen, Leipzig, 1862. 
