TABLE OF CONTENTS. XV 



Page. 



. 37. The Octahedron with a square base, 22 



. 38. The Octahedron with a rectangular base, .... 22 



. 39. The Octahedron with a rhombic base, .... 23 



.40. The right square Prism, 23 



.41, The right rectangular Prism, 24 



. 42. The right rhombic Prism, 25 



. 43. The right oblique-angled Prism, 25 



.44. The oblique rhombic Prism, 26 



. 45. The doubly oblique Prism, ...... 27 



. 46. The Rhomboid, 29 



. 47. The regular hexagonal Prism, 31 



Consideration of the changes to which the Primary Forms of 

 Crystals are subject. 



. 48. Modifications of Primary Forms, 31 



. 49. Kinds of Modifications, 32 



. 50. Disposition of Secondary Planes regulated by symmetrical 



Laws, 33 



.51. Passage of one Form into another, 48 



Of the imperfections of Crystals in respect to their Form. 



. 52. Kinds of Imperfection in Form, 56 



. 53. Irregularities depending upon the Formation of the Individu- 

 als themselves, 56 



. 54. Irregularities from contact with other Individuals, . . 58 



.55. System of Crystallization, .59 



. 56. Series of Crystallization, 60 



. 57. Methods for ascertaining the Angles of Crystals, . . 61 



.58. Structure, 68 



. 59. Cleavage, 68 



$, 60, Cleavage Planes, .69 



