MAGNETISM AT HALIFAX, AUGUST, 1904. — DIXON. 255 



maojnetic rocks and " the lines which we draw on the surface of 

 a map as those to which the north pole is attracted, may, in 

 fact, roughly represent the ridge lines of concealed masses of 

 magnetic rocks." *^^ In all countries such magnetic ridges have 

 been noticed, and geologists now recognize fully the great 

 importance of magnetic work. As an example of this, it may 

 be noted that the magnetic surv^ey of Maryland was inaugurated 

 by the State Geologist, Professor W. B. Clark, and a very large 

 share of tiie expenses was borne by the Maryland Geological 

 Survey. This survey, which was carried out by Dr. L. A. 

 Bauer (1896-1900) is by far the most complete in America, in 

 fact the only country which has been surveyed with more detail 

 is Holland. 



In Japan, a recent magnetic survey has been made (1893- 

 1896) and the three elements have been measured at more than 

 320 stations well distributed over the Islands. This survey was 

 carried out under the Earthquake Investigation Committee and 

 the results were published this year.*^^ The maps have been 

 no arranged that it is possible to compare the distribution of 

 magnetic force with the geological structure of the country. 



Magnetic Pros])cciivg for Iron Ores. 

 Riicker's observations on the assistance to be derived from 

 magnetic surveys in studying the geology of a country, were 

 anticipated in 1843 by Van Wrede, who first saw that mag- 

 netic work should furnish valuable information with regard to 

 the location of magnetic deposits. Practically nothing resulted 

 from this till in 1879 Professor Robert Thalen published a 

 paper " On the examination of iron ore deposits by magnetic 

 measurements," and since then much work has been done in 

 this direction in Sweden. In Canada also some valuable work 

 has been done by the Geological Survey and Department of 

 Mines. In the geological report for 1903*^' we find an inter- 



(1) A. W. Riicker, Terrestrial Magnetism, vol. iii, p. 42. 



(2| A niagnelie survery of Jap«n, epoch 1895. A. Tanakadate. Journal of the Col- 

 lege of Science, Imperial University, Tokyo, 1904. 



(3) Summary Report of Geological Survey of Canada for 1903, p. 122. 



