MINERAL CONSTITUENTS OF ROCKS. 61 



silica 2-12, and oxyds of iron and manganese, etc., 3-46. In No. 6, the 2-80 is mag- 

 nesia. 



The enamel of teeth contains 85 to 90 per cent, of phosphate of lime, 2 to 5 of car- 

 bonate of lime, and 5 to 10 of organic matters. The shells of a fossil Obolus afforded 

 Kupffer the composition nearly of a fhior-apatite (Am. Jour. Sci., III. vi. 146). 



Fish-scales from a Lepidosteus afforded Fremy 40 percent, of organic substance, 51*8 

 of phosphate of lime, 7-6 of phosphate of magnesia, and 4-0 of carbonate of lime. 

 Other fish-scales contained but a trace of the magnesia-phosphate and more of organic 

 matters. 



The ashes of ordinary meadow-grass afford 8 percent, of phosphoric acid; of rye 

 straw, 4 per cent. ; of clover, 18 per cent. ; of wheat and rye, 50 per cent. ; of peas and 

 beans, 33-38 per cent. ; of sea-weeds of the genus Fucus, l - 2 to 4 per cent. ; of the genus 

 Laminaria, 3*4 to 5 per cent. (Schweitzer); of the species Iridea edulis, 11-4 per cent. 

 (Forchhammer). 



Phosphatic nodules, possibly coprolitic, in the Lower Silurian rocks of Canada (on river 

 Ouelle), afforded T. S. Hunt (see Am. Jour. Sci., II. xv. and xvii. ), in one case, phos- 

 phate of lime, 40-34, carbonate of lime, with fluorid, 5-14, carbonate of magnesia 9-70, 

 peroxyd of iron, with a little alumina, 12-62. sand 25 44, moisture 2-13 = 95-37. In a 

 hollow cylindrical body from the same region, there were 67 '53 per cent, of phosphate. 



Analyses of Coprolites (Fossil Excrements). — Nos. 1 and 2 by Gregory and 

 Walker; 3 and 4 by Connell; 5 by Quadrat; 6 by Rochleder (a coprolite from the 

 Permian). 



1. 

 Burdie- 

 house. 

 Phosphate of lime ... 9 -58 

 Carbonate of lime . . . 61-00 



Silica ) 



Organic material . . . . ) 

 Carbonate of magnesia . . 13-57 

 Sesquioxyd of iron ... 6-40 



Alumina - 



Water 5-33 



Lime of organic part . . - 

 Chlorid of sodium ... - 



2. 



3. 



4. 



5. 



6. 



Fife- 



Burdie- 



Burdie- 



Kosch- 



Oberlan- 



shire. 



house. 



house. 



titz. 



genau. 



63-60 



85-08 



83-31 



50-89 



15-25 



24-25 



10-78 



15-11 



32-22 



4-57 



trace 



0-34 



0-29 



0-14 



_ 



3-38 



3-95 



1-47 



7-38 



74-03 



2-89 



- 



- 



- 



2-75 



trace 



- 



- 



2-08 



_ 



- 



- 



- 



6-42 



- 



3-33 



- 



- 



- 



- 



- 



- 



- 



- 



144 



- 



- 



- 



- 



1-96 



100-01 97-45 100-15 10018 99-13 100-00 



(4.) Carbonaceous. — Mineral coal consists mainly of carbon, with some hydrogen 

 and oxygen, traces of nitrogen, and more or less of earthy impurities called the ash. 

 The hydrogen and oxygen are supposed to be combined with part or all of the carbon, 

 so that most coal consists of oxygenated hydrocarbons. When heated, they usually af- 

 ford much volatile matter, although containing none, this arising from the decomposition 

 by heat of some of the hydrocarbons present: the volatile matter is mostly hydrocarbon 

 oils (some kind of petroleum) or gas, with a little water. The dry porous carbon left 

 behind is called coke. Coals affording much volatile matter, and burning with a yel- 

 low flame, are said to be bituminous; and those affording little, and burning with a 

 a pale blue flame, non-bituminous. The varieties are: — 



A. Anthracite. — Non-bituminous, or nearly so. A hard, lustrous coal, breaking 

 with a conchoidal fracture and clean surface, and burning with very little flame, as the 

 coal of Lehigh, Wyoming, and other places of central Pennsylvania, also that of Rhode 

 Island. 



B. Bituminous coal. — Bituminous. Softer than anthracite, less lustrous, often look- 

 ing a little pitchy. The amount of volatile substances yielded varies from 10 to 60 

 per cent. 



a. Brown coal is black or brownish black coal, containing much oxygen, and occur- 

 ing in Mesozoic and more modern deposits. It is often called Lignite. True lignite re- 



