PKEPARATION AND MOUNTING 



be mounted in balsam in the usual manner, when it is equally 

 beautiful as a transparent or opaque object. From this it will be 

 seen that in many instances where a smooth stone is found suffi- 

 cient for the work (which is often the case when the section is 

 mounted in balsam) the final process of polishing advised above 

 may be dispensed with, as in the Orbitolite, Nummulite, &c., <fec. 

 It is quite necessary that the stones on which the objects are rub- 

 bed be perfectly flat, otherwise one side must be acted upon before 

 the other, and it will be found impossible to attain anything like 

 uniformity. Where it is not practicable to cut a section and the 

 object is very thick, a coarse stone may be first used to reduce it 

 and the smoother afterwards. 



The consideration of the cutting of sections from shells would 

 scarcely be deemed complete without some mention of what Dr. 

 Carpenter terms the decalcifying process. Muriatic acid is diluted 

 with twenty times its volume of water, and in this the shell is im- 

 mersed. After a period, differing according to the thickness of 

 the shell, the carbonate of lime will be dissolved away, and a pecu- 

 liar membrane left, showing the structure of the shell very per- 

 fectly. This may be mounted dry, in balsam, or sometimes in 

 liquid, according to the appearance of the object; but no rule can 

 be given. The discretion of the student, however, will enable him 

 to choose the most suitable method. 



From some shells it is easy to divide thin plates, or " laminae," 

 which require nothing but mounting in Canada balsam to show 

 the texture very well. In working, however, with those which 

 are " pearly," it will be found that experience and patience are 

 needed, as they are very brittle and peculiarly hard ; but a little 

 practice will overcome these difficulties. 



Amongst the Echinodermata, which include the star-fishes, sea- 

 hedgehogs, &c., there are many whose outer surface is covered 

 with " spines," or thin projections. Some of these are sharp and 

 thorn-like, others blunt, longer or shorter, and, indeed, of endless 

 variety. In many of these, when a section is made, rings are 

 seen which have a common centre, with radiating supports, re- 

 sembling sections of some of the woods. These are very beauti- 

 ful objects, and methods of procuring them may now be con- 

 sidered. It is the best to cut as thin a section as can safely be 



