Correspojidence. 323 
Schuchert, Charles. 
On the Lower Silurian (Trenton) fauna of Baffin land. (Proc. U. 
S. Nat. Mus., vol. 22, pp. I43-I77, plates XII-XIV, 1900.) 
Simonds, F. W. 
"Floating sand," "Floating stones." (Science, vol. XI, p. 510, 
Mar. 30, 1900.) 
Spurr, J. E. 
Classification of igneous rocks according to composition. (Am. 
Geol., vol. 25, pp. 210-234. April, 1900.) 
Stevenson, John J. 
The section at Schoharie, New York [abstract]. (Bull. Geol. 
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Suess, E. 
Asymmetry of the northern hemisphere (Bull. G. S. A., vol. Ii, 
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Walcott, C D. 
Random, a pre-Cambrian upper Algonkian terrane. (Bull. G. S. 
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White, I. C. 
Edward Orton, with portrait and bibliography (Am. Geol., vol. 
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Wieland. G. R. 
Skull, pelvis and probable relationships of the huge turtles of the 
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Winchell, N. H. 
Twenty-fourth (and final) annual report on the Geological and 
Natural History Survey of Minnesota for the years 1895- 1898, pp. 284, 
Minneapolis, 1899.) 
Wooster, L. C 
The geological story of Kansas, i2mo, pp. 139. Crane and Com- 
pany, Topeka, Kansas, March, 1900. 
CORRESPONDENCE. 
The Causes of Ore Deposits. The solution of many per- 
plexing problems concerning the genesis of ore deposits has 
recently received great aid from an unexpected quarter. The 
application of the microscope to the rocks and the con- 
sequent great advancement in our knowledge of rock metamorphism 
has been the means of opening up a new field of ore studies. In 
the paper lately read by professor Van Hise* before the Washington 
*Some Principles Controlling the Deposition of Ores, By C. R. 
Van Hise. (Trans. American Institute of Mining Engineers, Wash- 
ington meeeting, February, 1900, 126 pp., 1900.) 
