Geology and Mineralogy. 333 
. 8vo. London, 1878. (Taylor & Francis.)—-The third 
matter of surprise and regret that the wan should be sonipeael 
S. 
to call for more subscribers to insure its continued su 
10. The Study of Rocks; An PTI bbeiels of r Patrolegy 
eh Frank Rutiey, F.G. Ss. iy he Geological Survey. 319 
12mo. London: 1879. cnatie Green & Co.).—The study of 
rocks by the microscope is now recognized as so important a part 
of lithology and so universally employed, that an English 
text-book giving the methods employed cannot fail to be appre- 
ciated. The work is about equally divided between the descri 
the rocks themselves. Mr. Rutley’s work is a samba one 
for the student. It is not, however, free from errors; the descrip- 
tion and figure on page 94 ee that the mineral oiteved to must 
be mier ocline and not orthoc 
11. Ueber 
the amount of alkalies present. He finds that many of the previ- 
ous analyses are incorrect in the determination of the lithia, and 
ak 
(this Journal, Ill, xvii, 176). For the lepidolite of Paris, 
I 
Rozena, ommelre writes the formula R,AlSi,0 AS ges Ak, 
out ‘Oct. 28, 1878.) 
nm the colguntion of Spodumene and Petalite; by Cc 
Deal r.—Dr. Doelter has recently analyzed spodumene from 
Norwich, h, Mase, (1) and from Brazil (2) "with the following 
acm #10, FeO CaO MgO Ii,O Na,O K,0O 
(1) 63-79 27:03 0°39 0°73 0:21 7:04 1°10 0°12=100°41 
(2) 63.34. 2766 115 069 ... 709 098  ..=100°91 
After making allowance for impurities, he obtains for the 
Lf . 
quantivalent ratio of R: Al: Si=1:3: 8 (instead of 1: 4:10 previ- 
I I 
ously accepted) and writes the formula R,AISi,O,2, where R=Li 
a 
a in the ratio of 15: 
The compre of petalite i is also discussed and the conchae 
‘acoxe ior, (Com .—Mr. E. 
vhs of Cleveland has identified cacoxenite on the martite 
erior. It appears in brownish-yellow acicular crystals 
Pia radiating tufts. 
