Geology and Natural History. 205 
poeible, add a piece of ammonic-fluoride about the size of a pea; 
oisten the whole with a few drops uf se ig ee _sulphurie 
Ad 
given. Sometimes this second fusion requires to be repeated, but 
for practical purposes this is unnecessary if the previous operations 
have been well conducted. The bulk of all three filtrates need 
hot be over 200 c.c. The chromium may be estimated by geonnen | 
acidifying the solution, reducing the chremium to the state o 
sesquioxide by means of s sulphurous acid solution, and oii 
by ammonic hydrate. If the Bunsen method of filtration is use ed, 
the ] moun 
angan 
from the alkaline solution. One advantage of this method is, that 
there i is no troublesome SyAperNe required to separate silicon. 
sults of parallet analyses 
1. C mite = —-2888 per cent Cr,0, 50°450 
2868 per cent Cr,0, 50°627 
Tam confident that with more experience still better results may 
tained. 
be ob 
II. Gronogy anp Natural History. 
1. Address to the American Association for the Advancement 
A pe soience, by Tuomas Srerry Hunt, LL.D., on retiring from the 
ce of President of the Association, "Indianapolis, Aug, 16, 1871. 
ta bp. 8vo.—Dr. Hunt takes for the themes of his address, first the 
ae, of the Appalachians, especially the history of researches 
ers in connection wi 4 own, and also the Ame 
Which he has been led. He first oe the crystalline rocks of 
the chain into hak series, draws out the distinctive chological 
‘teristics of each, pcs aintains sre they belong to differ- 
®at geological eras, 
a Adirondack me Lada Series, = is marked by 
granitic gneisses, e 
eddi eisses, often coarse-grain generally 
— or grayish in "color, . “often — and little —- 
_ CeOus, » and including reat eds of magne etic re, and tie 
Raphite but a argillites, or slates caine staurolite, 
andalusite or cyani 
