496 L. A. Bauer — Wilde's JExjylication of the Secular 



both processes. The objection has often been raised against 

 the theory of original deposition that it does not account for 

 ores associated with deep sea rocks.* But why should not the 

 shore and deep sea deposits of ore be formed by entirely dif- 

 ferent processes? If the drainage waters of any area discharge 

 so much iron into the sea that sediments formed at long dis- 

 tances from shore contain sufficient iron in twenty or thirty 

 feet vertically to form two feet of the ore by concentration, 

 these same drainage waters must deposit great quantities of 

 iron both chemically and mechanically along the shore line. 

 Thus, the accumulation of both shore and deep-sea deposits of 

 iron would go on simultaneously, but the latter would require 

 a secondary concentration to render them of practical value. 

 Geological Laboratory, Hamilton College, Clinton, N. Y. 



Art. LXII. — Wilde's Explication of the Secular Variation 

 Phenomenon of Terrestrial Magnetism / by L. A. Bauer, 

 C. E. 



[Read before the Philosophical Society of Washington, Feb. 27, 1892.] 



In 1871 Prof. Hornstein of Prague made known his dis- 

 covery of a periodic change in the magnetic elements of 26|- 

 days, almost exactly equal to the synodic rotation of the sun, 

 as deduced from the equatorial sun-spots. It was then said 

 that "this method of discovering the time of .rotation of the 

 unseen solid body of the sun by its effects on the magnetic 

 needle was the first installment of the repayment by Magnet- 

 ism of its debt to Astronomy." And true it was. For three 

 centuries a vast amount of time and money has been spent 

 on terrestrial magnetism. It has engaged the most brilliant 

 minds. Money and industry have not been wanting. Zeal and 

 enthusiasm have not been wanting. The numerous mag- 

 netic observatories already established and the vast bulk of 

 observations already accumulated will bear ample witness. 

 We are, however, still only on the threshold of this mighty 

 subject and have not yet learned its very alphabet. " The 

 held of investigation into which we are introduced by the 

 study of terrestrial magnetism is as profound as it is exten- 

 sive,' 1 says Maxwell. '' What cause," inquires he, " whether 

 exterior to the earth or in its inner depths, produces such 

 enormous changes in the earth's magnetism, that its magnetic 

 poles move slowly from one part of the globe to another ? 



*J. P.Kimball: Genesis of Iron Ores by Isomorphous and Pseudomorphous 

 Replacement of Limestone. American Geologist, viii, p. 352. 



