CONSTITUENT MINERALS OF ROCKS. 67 



In many shells the inner pearly layer consists of carbonate of lime in the 

 condition of Aragonite (§ 69) ; while the outer (or the whole, if no part is 

 pearly) is usually common carbonate of lime, or calcite. The spines of Echini 

 are calcite. 



In corals of the genus Millepora, according to Damour, there is, besides car- 

 bonate of lime, some carbonate of magnesia, amounting in one species to 19 

 per cent., while but little in others. These corals have been shown by Agassiz 

 to be related to the Medusae, and not to the ordinary polyps. Forchhammer 

 found 6.36 per cent, of carbonate of magnesia in the Isis nobilis, and 2.1 per 

 cent in the Corallium nobile, or precious coral of the Mediterranean. 



The Nullipores and Corallines are vegetation having the power of secreting 

 lime, like the coral animals. The shells of Rhizopods (called also Polythalamia 

 and Foraminifera) are calcareous. 



The shell of a lobster (Palinurus) afforded Fremy, Carbonate of lime, 49.0, 

 phosphate of lime, 6.7, organic substance, 44.3. 



76. (2.) Siliceous. — The organic Silica is, in part at least, in that condition 

 characterizing opal (p. 55.) The mineral Randanite is a kind of opal, made of 

 infusorial remains. 



77. (3.) Phosphatic. — Analyses of bones: 1, 2, human bones, according to 

 Frerichs; 3, fish (Haddock), according to Dumenil; 4, shark (Squalus cornu- 

 bicus), according to Marchand ; 5, fossil bear, id. 



1. 



Phosphate of lime 50.24 



Carbonate of lime 11.70 



Sulphate of lime 



Organic substance 38.22 



Traces of soda, etc 



Fluorid of calcium 



Phosphate of magnesia 



2. 



3. 



4. 



5. 



59.50 



55.26 



32.46 



62.11 



9.46 



6.16) 





13.24 





4.44 



12 25 



30.94 



37.63 



58.07 



4.20 





1.22 



3.80 









1.20 



2.12 







1.03 



0.50 



In No. 4 a little silica and alumina are included with the fluorid. No. 5 con- 

 tains also silica 2.12, and oxyds of iron and manganese, etc., 3.46. 



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

 carbonate of lime, and 5 to 10 of organic matters. 



Fish -scales from a Lepidosteus afforded Fremy 40 per cent, of organic sub- 

 stance, 51.8 of phosphate of lime, 7.6 of phosphate of magnesia, and 4.0 of phos- 

 phate of lime. Other fish-scales contained but a trace of the magnesia-phosphate 

 and more of organic matters. 



Phosphatic nodules, possibly coprolitic, in the Lower Silurian rocks of Ca- 

 nada (on river Ouelle) afforded T. S. Hunt (see Am. Jour. Sci. [2] xv. and xvii.), 

 in one case, phosphate of lime, 40.34, carbonate of lime, with fluorid, 5.14, car- 

 bonate 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). 



