WILLIAM B. DWIGHT. | 67 
more opaque details, until their structure is also suf- 
ficiently translucent, avoiding any further abrasion of 
the delicate structure. This may be done by using a 
small stick, having a very small squared end, but with 
its edges a little rounded. Have a little emery mud ina 
saucer near your hand; dip the end of the stick in it, 
and gently rub it on the portion of the structure to be 
further abraded, holding the specimen in the left hand, 
against the light, so that you can see exactly where to 
work. For very narrow structures, the end of a common 
square match-stick is of the right size ; but often a larger 
stick is better. Still better, where it is not too large, the 
flat head of a small copper nail is excellent, as it works 
rapidly. But frequent rinsing of the slice will be 
necessary to examine the progress of the work, and much 
care to avoid abrading a hole in the thinner contiguous 
portions. 
The second infelicity in the general methods of rock- 
slicing is the contentment with the preparation of the 
usual very small sections, rarely more than seven-eighths 
of an inch square, often considerably smaller. ‘The New 
York State Survey is doing excellent work in the prepa- 
ration of very large sections, which is greatly to be com- 
mended. It is possible that the United States Geological 
Survey may also prepare large sections ; but the general 
apathy of scientists with respect to the importance of 
such sections is strange. 
It seems to be the common, but entirely erroneous, as- 
‘sumption that a small slice, no bigger than a thumb nail, 
may be considered a fair sample of a specimen which is, 
_ perhaps, as big as a fist. Toa very considerable extent 
this is very probably true in the making of lithological 
‘slices ; though even in this special line I believe it to be 
a wrong assumption with reference tocertain points of re- 
search. This question will have further consideration a 
dittle later. 
17 
