MANUAL OF NATURAL HISTORY. 687 



quisite for a general examination of rocks and soils, 

 or for testing mineral springs. A few other proper- 

 ties of minerals may be attended to, as the streak, 

 hardness, fusibility, colour, transparency, fracture, &c., 

 but the study of their other physical and optical 

 qualities must be reserved for the return home. 



For travelling purposes, collections of type mi- 

 nerals for illustrating different properties, are now 

 prepared. Among the more useful are sets exhibit- 

 ing degrees of hardness, fusibility, and cleavage, 

 which can be procured at a very reasonable rate from 

 Mr. S. Highley, 32, Fleet-street, London, where 

 may likewise be obtained models in wood or glass 

 illustrative of crystallographic forms, and shewing 

 the principal geometric shapes assumed by simple 

 minerals. 



Isolated specimens of rocks are of little or no 

 value, while, on the other hand, series of examples 

 are highly instructive and important. It is of very 

 great consequence that the locality be known, there- 

 fore the collections of one day should not be allowed 

 to interfere with those of the next, but should be 

 carefully labelled and packed up on the same evening. 

 Specimens should not be too small, those of rocks 

 should be about two or three inches square, but 

 when any gems or precious minerals are discovered, 

 they should always be secured irrespective of size. 

 With regard to fossil remains, however, the case is 

 quite different, as every fragment should be secured, 

 as most valuable to science, species and genera 

 having been established on almost a single bone. 



