XV. — GEOLOGY AND MINERALOGY. 125 



intimately mixed with gold in small seams in porphyry. Its 

 composition and its association with that metal are remarkable, 

 and it has been provisionally placed in the case containing speci- 

 mens of Gold. 



A collection of Gold and Silver Ores and a collection of 

 Meteorites purchased in 1888 with some other well known 

 minerals will be found in their respective subdivisions. 



II.— COLLECTION OF WOODEN MODELS OF CRYSTALS 

 AND CRYSTALLIZED MINERALS. 



This collection occupies the two large central show cases ; it 

 consists of 743 wooden models arranged according to the six 

 systems of Crystallography, namely : Cubic, Tetragonal, Hexa- 

 gonal, Rhombic, Oblique, and Triclinic or Asymmetric. 



In order to make this collection useful and interesting, even 

 to those unacquainted with the subject, the faces of the models 

 have been painted in colours to show the different forms, which 

 are usually found combined in each system in a more or less 

 complicated manner. 



For instance, in the Cubic System, a simple form, the 

 Octahedron, is painted white on its eight faces, so that, consider- 

 ing only the holohedral forms on the left side of the tray, every 

 complex form in which the octahedron enters into combination 

 with other forms, will be known at a glance, and so on for 

 others ; while the models of the simple ones, eight in number, 

 will be easily distinguished by being of only one colour. 



On the right side of the tray are placed the models of 

 hemihedral forms, so-called because they have only half tlie 

 number of faces of the corresponding holohedral forms, the 

 simplest being the Tetrahedron, of four faces, corresponding to 

 the Octahedron. 



This collection of models has been illustrated by good examples 

 of natural crystals, which are placed in the same tray as the 

 crystallographic system to which they respectively belong. For 



