200 ROCHESTER ACADEMY OF SCIENCE. [| June 22, 
minerals. The outer part will be white with quartz, then comes a 
reddish band with garnet, then a black band with titaniferous iron and, 
finally, (if magnetite is not present, or if it has been removed with a 
magnet) a white band with zircon, or white and yellow if monazite is 
also present. This grouping, in which the range of specific gravity is 
from 2.5 to 5 only, well illustrates the delicacy of the process. Indeed, 
by skillful manipulation minerals differing so slightly in specific gravity 
as titaniferous iron and monazite (4.7 to 5) can be almost completety 
separated when the process is facilitated by a slight difference in the 
size of the grains. Usually, however, it will be found best to make 
the separation in the batéa at about sp. gr. 3, throwing away the greater 
part of the quartz and feldspar and retaining all the heavier elements 
for further sub-division with heavy liquids. 
The whole operation, from the preliminary crushing to the mount- 
ing of a microscopic slide, can be performed in a few minutes, usually 
in less time than is required to prepare a rock section. Thus the least _ 
abundant accessories can be determined as quickly and readily as the 
essential elements, since they appear completely isolated in numerous 
specimens and with clearly defined crystalline outlines. Accessories 
so rare that only half a dozen grains or less occur in an ordinary 
hand specimen will often be found. 
The application of the batéa in the laboratory in the preparation of 
material for microscopic study and for chemical analysis is too obvious 
to require farther mention. A somewhat extended series of observa- 
tions indicate that it will prove even more valuable in work which is 
more strictly geological. This application depends on the two following 
conclusions, based on several hundred tests of Brazilian rocks, that will 
presumably be found to hold good for other parts of the world : 
ist. Most of the prominent rock groups afford residues which are 
characteristic, either through the presence of accessories peculiar to 
each group, or by the relative abundance, or peculiarities of form and 
structure, of those that are common to several groups. 2nd. Many of 
the most common heavy accessories are practically indestructable and 
can therefore be recovered in recognizable form even when the rocks 
or their debris are so completely altered that their original type is not 
otherwise recognizable. 
Possibly with more extended observations the first conclusion will 
not be found to be general. This, however, will scarcely detract from 
its value if the geologist finds that in his limited district he can identify 
the rock types by their residues,.as he has in them a means of forming 
a definite opinion regarding many rock masses that otherwise would 
