222 Microscopical Examination of Rocks. ~ [April, 
ordinary 3 dy 1 zwch, asa slide 45 mm. by 25 mm.can be rotated on 
the table of the microscope; besides they are less liable to break 
in dropping them, and also take up less room. 
In the New York State Museum of Natural History the slide 
measuring 45 mm. by 25 mm. is adopted. As it was found that 
this glass slide was too small for a number of sections of fossils, 
which exceed the usual size, two other standard sizes were intro- 
ae 
i 
duced which are in proportion to the first. Size B is twice the — : 
size of first — 50 mm. by 45 mm. Size C is twice the size of sec- 
ond — 50 mm. by 90 mm. It would be of great advantage if a 
uniform size was introduced in the various collections of those 
whe prepare sections. The slide 45 mm. by 25 mm. is generally 
adopted with lithologists and palzontologists both in America 
and Europe. 
Process of Slicing and Grinding —The fossil or rock is at first 
marked with a pencil and afterwards with a file in the direction in 
which it is designed to be cut. It is then held with the right 
hand without any further apparatus, in such a direction that the 
revolving slicer will cut the specimen according to the marked 
line. The slicer is constantly supplied during the operation with 
flour of emery and water. If there is plenty of material and no 
special direction needed, small slices can be separated from the 
rock by a heavy blow with a hammer. The rock fragments k 
should as a rule not be beyond the size of a twenty-five cent 4 
piece; of course it is of great advantage to prepare sections 
which offer a large field for observation, and the rock specimens 
should not be chosen too small, as they lose in size during the 
grinding process. 
The slice of rock which has been separated either by the slicer 
or by the heavy blow with a hammer, is gently pressed with the 
right hand against the turning plate A, while the left hand sup- 
plies plate A with emery A and water. It is necessary to change 
constantly the position of the rock-slice in the right hand in order — : 
to grind it to an even and plain surface. The slice is then well a 
rinsed and cleaned of any particle of emery A, and then trans- — : 
ferred to plate B (emery B) where the grinding proceeds till its 
surface is free of any scratches. Being cleaned of the emery — 3 
B, it is brought upon glass plate C (emery C) and ground till its — a 
surface is entirely smooth. The rock section is finally well i 
rinsed and brushed to clean off all impurities and allowed S 
to dry. 
