68 PREPARATION OF SECTIONS OF ROCKS AND MINERALS. 
But in slices of paleontological specimens, there can be 
no doubt not only that very large sections—that is, of 
from two to four square inches—are much to be preferred 
where attainable, but that with reference to many classes 
of organizations, they are the only slices upon which a 
true knowledge of the organism can be predicated. 
Two chief reasons may be presented in justification of 
this assertion. 
First—It is impossible to tell beforehand what portion 
of the paleontological specimen may microscopically 
present the structure of the organism in its most com- 
plete form, or in the best state of preparation. Chipping 
off a small splinter and slicing it is simply a lottery, not 
up to the dignity of true scientific research. It may hit 
a very perfect portion of the structure, or it may hit a 
spot, which, however favorable it appeared macroscopi- 
cally, is inferior, microscopically, to other parts of the 
specimen. 
But if a large slice, of two, three or four square inches, 
is made, a large field is at once presented, from which a 
selection can be made of the best-preserved portions, if 
it is not desirable to mount the entire slice. 
In the second place, the different variations in the type 
of the structure may be entirely lost in the smaller frag- 
ment while the larger section may present them in com- 
bination, and thus prove their unity and the identity of 
the species. 
I may illustrate this best by an actual experience of 
my own. In endeavoring to study some fossiliferous 
Trenton specimens, containing the same microscopic coral 
above mentioned, there appeared, to myself and other 
paleontologists, to be at least three separate species pres- 
ent ; one, a sponge, and two corals of a different genera. 
There was nothing to disturb the view’so long as slices 
of the ordinary small size were made. But as soon as 
large sections of a single coral-colony were made, it be- 
18 ? 
