Geology and Mineralogy. 243 
6. Manual of Mineralogy and Lithology, containing the 
elements of the science of Minerals .and Rocks for the use of the 
practical Mineralogist and Geologist and for instruction in Schools 
and Colleges; by Jamus D. Dana, 4th edition, 518 pp. 8vo, New 
York, 1887 (John Wiley and Sons).—This new edition of the 
author’s “ small” mineralogy, like the preceding, places together, all 
the ores of the same metal, and in this and other ways the Manual is 
adapted to the needs of the mining and practical mineralogist. 
As the preface states, the work has been revised throughout, and 
brought down to the year 1886 in its descriptions and in the in- 
troduction of new species; and the chapter on Rocks has been 
revised, rearranged, much enlarged, and supplied with additional 
illustrations. 
7. On the chemical composition of the orthoclase in the Cort- 
landt Norite. (Communicated.)—Since the publication of the 
writer’s description of this interesting mineral in the February 
number of this Journal (p. 139), a complete analysis of it has 
been made by Mr. Wm. M. Burton of the Chemical Laboratory 
of the Johns Hopkins University. The results are worthy of 
publication as placing beyond all doubt the nature of the mineral 
in spite of its very unusual association. 
The material for analysis was separated by the Thoulet solu- 
tion, all that portion of the rock being used which possessed ‘a 
specific gravity of 2°62 or less. The results of two complete 
analyses of lead fusion (I-II) and one partial analysis of fusion 
with potassium and sodium carbonate (III) are as follows: 
1.) (II.) (IIT.) (Mean.) 
SiO, 61°71 61:76 61°65 61°71 
Al,O3 21°50 21°36 21°55 21:47 
CaO 2°82 2°70 pee 2°76 
K,0 12°74 12°88 Lae 12°81 
Na.0 88 1:04 Urea 96 
Total 99365 99°74 pei 99°71 
Now on account of the very intimate admixture of the ortho- 
clase with the accompanying and included andesine, it was doubt- 
less impossible to perfectly.separate the two minerals, as is made 
more probable by the specific gravity which is somewhat high for 
orthoclase. If, therefore, we deduct from the above mean analy- 
sis the amounts of SiO, and <AI,O, necessary to satisfy the 2°76 
per cent of CaO and 0-96 per cent of Na,O in the anorthite and 
albite molecules respectively, we obtain: 50°23 per cent SiO,, 
14°75 per cent Al,O, and 12°81 per cent K,O; and these propor- 
tions, calculated as percentages, give: SiO, 64°57, Al,O, 18°96, 
K,O 16-47, while the proportions calculated from the formula 
K,Al,Si,O,, are: SiO, 64:68, Al,O, 18°43, K,O 16°89. 
GEORGE H. WILLIAMS. 
Baltimore, Feb. 18th, 1887. 
