18 THE NORTHERN MICROSCOPIST, 
only their structure, but frequently their origin; applied te the sedimentary 
rocks it tells whether they are organic or inorganic, and what and how great 
alterations they have undergone since their deposition ; besides bringing to our 
knowledge myriads of minute animals which have helped to build up many a 
vast formation, and of which, without the aid of the microscope, we should 
have remained ignorant. 
Few objects for the microscope possess so much beauty as sections of rocks. 
If igneous, for the most part they are filled with crystals which glow with 
gorgeous colours when viewed with polarised light ; if sedimentary, the field of 
the microscope often filled with tiny shells of exquisite form, showing us at one 
glance both the inhabitants and builders of a former world. 
To prepare sections of rocks is by no means a difficult task. A cumbrous 
and costly machine is unnecessary. Sections, good and satisfactory in every 
way, may be prepared with very simple apparatus. This consists of the follow- 
ing: I, an iron plate, about twelve inches square ; 2, a coarse gritstone; 3, a 
Water-of-Ayr stone; 4, an Arkansas stone; 5, old Canada balsam (this cannot 
be too old); 6, a bottle of benzol or turpentine ; 7, solution of balsam in benzol ; 
8, moderately coarse emery ; 9, flour emery, or common knife polish; 10, a 
glass plate, about six inches square, common window glass, if with a level 
surface, will do. 
I. Preparing sections of hard rocks: In the first place a thin chip must be 
procured by the use ofa hammer. This chip should be about one inch square, 
and not more than one-eighth inch thick. Chips of sedimentary rocks may be 
thicker. Rub the chip down by hand with emery and water on the iron plate, 
until one side is perfectly flat. To remove scratches, next rub the chip ona 
glass plate with fine emery, and polish on the Water-of-Ayr stone. When 
quite smooth, wash it well, and let it dry. Meantime place some of the old 
balsam on a glass slip, and warm it over a lamp until all the more volatile parts 
of the balsam evaporate, so that, on cooling, it becomes hard and tough. Do 
not let the balsam boil. When the balsam is properly hard, warm the chip 
gently over the lamp, or on a hot metal plate, brush it over with a little turpen- 
tine, and re-melt the balsam. Then lower the chip slowly into the balsam until 
it is cemented firmly and evenly by its flat surface to the glass slip. When the 
balsam is quite cold, the chip is to be rubbed down on the iron plate with coarse 
emery until it is too thin to bear any further rough friction. With care many 
rocks may be brought to the requisite thinness on the iron plate alone, and will 
require little finishing. The necessary degree of thinness will vary according 
to the nature of the rock ; but, as a general rule, most hard rocks must be cut 
thin enough to read through when placed on the page of a book. When the 
section will no longer bear the friction of the coarse emery remove it to the 
glass plate, and grind it thinner with flour emery, and finally finish it off on the 
Water-of-Ayr stone. The slide, at the finish, will be disfigured by deep 
scratches from the emery, and the section must be transferred to a clean slip. 
Warm the section enough to melt the balsam, and push the section off with a 
needle into a cup of turpentine, and wash carefully with a small brush. Now 
pour a little balsam and benzol solution on the clean slip, place the section upon 
it, add a little more balsam, and cover. 
II. Preparation of soft rocks and sedimentary rocks generally: These are 
prepared and mounted in the same way as hard rocks but no emery is to be used ; 
they must be ground down and finished on the three stones mentioned above. 
Some very friable rocks will require a preliminary hardening by immersion for 
some days in a solution of I. baisam in benzol. The balsam must be first 
baked in a cool oven, until on cooling it becomes hard and brittle ; then dissolve 
it in benzol; or 2., in a solution of shellac in alcohol. ‘This is, perhaps, the 
better of the two. When the chip has remained long enough in the solution, it 
must be dried in a warm place, Sedimentary rocks, as a rule, do not require 
