PREFACE. XI 



tions of the species, but also for producing a gene- 

 ral survey of the combinations most commonly oc- 

 curring among the simple forms found in nature. 

 They are disposed in the order of the systems of 

 crystallisation, and provided on the opposite page 

 with the explanations given in crystallographic signs. 

 The figures in the last five plates are not ar- 

 ranged in this order, since they were added only 

 in the course of printing the work. They refer 

 either to some remarkable varieties of species de- 

 scribed in the system, or they have been rendered 

 necessary by the reception of several species into the 

 first Appendix, which had been described by vari- 

 ous authors, the greater part of them since the pub- 

 lication of the German original. 



In comparing many of these with nature, the 

 cabinet of Mr ALLAN, as will appear from the 

 frequent references made to it, has afforded the 

 translator the most important assistance; and he 

 trusts it will not be found out of place, if he embraces 

 the present opportunity of expressing to that gentle- 

 man, the deep sense he must ever entertain of the 

 many marks of kindness he has received from him. 

 To him he has not only been indebted for a home 

 in a foreign land, but also for much assistance, and 

 many valuable observations, in the progress of this 

 work. To Dr BREWSTER he is under the greatest 

 obligations, both for many interesting additions, 

 concerning the optical and other properties of mi- 



