FLUID METHODS OF SURVEYING BOREHOLES 



119 



places where the magnetic needle would be useless. Such 

 places are, of course, in iron fields and certain of the basic 



johfL n 



Fig. 66. — Specimen borehole surveys by the Kiruna method. 



igneous rocks. Moreover, good instrumental work can 

 be done by the Kiruna method in holes of L4-in. diameter 

 after due allowance for cohesion and capillarity has been 



