WILLIAM B. DWIGHT. 69 
came evident that these three forms were all protean and 
remarkable variations of the same species of coral. 
With regard to petrographical specimens, while, as 
above stated, it may be conceded that in many eases a 
small chip would be a sufficiently fair specimen of the 
mass, this is not true in certain special lines of research. 
Consider, for instance, a case where the metamorphic 
alteration, or alteration by decomposition, of a certain 
kind of rock, is the subject of study. A small chip 
taken off accidentally, showing some most convenient 
edge, may fail entirely to exhibit some of the more in- 
structive changes of the specimen. But if one or more 
large sections are made, and these large fields are exam- 
ined, the most interesting and instructive points can be 
picked out, and there is far less chance that some of the 
most important exhibits may escape our vision. 
It may be supposed that the cutting of the large slices 
is generally impracticable. Such is not the case. With 
proper machinery (one form of which will be described 
in another paper), it is quite practicable and easy. The 
cutting of a large specimen of a limestone rock, or any 
soft rock, takes very little more time than the cutting of 
a small one, and the grinding down of either takes prac- 
tically about the same amount of exertion. 
I urge very strongly the propriety of the general pre- 
paration of much larger sections of paleontological speci- 
mens, and of certain groups of petrographical specimens 
than the usual sections now made. 
THE EXHIBITION AND DESCRIPTION OF NEW DEVICES IN 
MACHINERY FOR THE MAKING OF THIN SECTIONS OF 
MINERALS AND PALEONTOLOGICAL SPECIMENS. 
BY WILLIAM B. DWIGHT. 
After making some preliminary statements as to the 
entire lack of any machine capable of cutting thin slices 
19 
