212 SOILS AND MANURES 



is generally of inferior quality. The best qualities are, 

 as a rule, poorer than the lowest grades of Somme phos- 

 phate and rarely contain more than about 40 per cent, 

 of tricalcic phosphate. 



Caribbean or West Indian phosphates are sometimes 

 described as phosphatic guanos. Some of them are 

 properly so-called, being derived from guanos, but others 

 are of purely mineral origin. Deposits are found on 

 several of the islands and are named accordingly. They 

 have been extensively worked, and some of the richest 

 were exhausted soon after they were discovered. Eedonda 

 and Alta Vela phosphates are not phosphates of lime but 

 phosphates of iron and alumina. The former contains 

 only about 3 per cent, and the latter 11 per cent, of lime. 



Quantities of phosphates of fairly good quality are 

 also produced in various parts of South America, par- 

 ticularly Venezuela, Guiana, and Brazil. 



Coprolites. The name coprolites was first given by 

 Dr. Buckland to certain peculiar stones found in the 

 Gloucestershire lias, which had long been familiar and 

 were locally known, from their appearance, as fossil fir- 

 cones. .He described them as oblong pebbles, usually 

 about two to four inches long and half as thick some of 

 them are much larger varying in colour from ash grey to 

 dark brown or black. They exhibit a conchoidal fracture, 

 and the peculiar structure which shows that they have 

 passed through animal intestines. They appear to con- 

 sist of the fossilised excrement of certain extinct reptiles 

 called Ichthyosauri, which infested the low-lying swampy 

 ground of Cambridgeshire and the eastern counties. The 

 term coprolite is derived from KOTT^OS (dung) and At0o? 

 (stone), literally dtingstone. They are found mixed with 

 the bones and teeth of fishes and sometimes even the 

 remains of the smaller species of Ichthyosauri. They 

 consist mainly of calcium phosphate, but are usually 



