144 JOURNAL OF THE [july, 



partment, take consolation in this : it is not by any means 

 absolutely necessary to be intimately acquainted with the intri- 

 cacies presented by the world of crystals, or the phenomena 

 of polarization in order to take up this study. If you can master 

 these things, if you can lift the veil of Isis, so much the better 

 for you, so much the greater the enjoyment which you will 

 derive, so much the more will you be enabled to accomplish for 

 science. But you may do a great deal without these things. 

 Many, if not most of the minerals, of which a rock is composed, 

 may be determined without a detailed, or even general knowledge 

 of crystallography, and it is not always, or even generally neces- 

 sary to resort to the polariscope in order to identify the con- 

 stituents of a rock. Happily, a number of other features, which 

 are quickly learned and easily remembered, help us in our in- 

 vestigation, and it is almost needless to add that before long 

 even those formidable subjects, crystallography and polarization, 

 lose much of their grim aspect. 



You will then be able to determine at a glance the principal 

 rock-forming minerals which you behold in a thin section, and 

 you will then also find that the microscopical investigation of 

 rocks affords you, in the endless variety of forms which it pre- 

 sents, in the gorgeousness of the colors which it reveals, in the 

 wealth of its unsolved problems, a greater, richer and fuller 

 field for study than any of the old and \vell-beaten paths of 

 animal and vegetable morphology. 



Even the general microscopist, the mere onlooker or collector 

 of specimens, might turn with advantage to this subject. It 

 will furnish him with some of the loveliest objects within the 

 whole domain of practical microscopy, and will open up to him 

 one of the most enchanting prospects in the wonderland of 

 science. 



