. The Crystal Falls iron-bearing district of Michigan. Iron ores; Geology; Geology, Stratigraphic; Geology, Stratigraphic. MAGNETIC! OKSERVATIOXS. 865 the zone of retardation and a lar«iCT over tlie ))oint of no liorizontal deflec- tion, uliicii correspond i-espeotively to the two niaji'netic i-ocks. If the two formations are parallel in strike, l)nt diii away from each other, the cnrves of the horizontal and vertical comjjonents for different anjrles of dij) and different relations of thickness and depth of coverino- are shown in figs. 19 and 20. In fig-. 19 the formations are widely separate
. The Crystal Falls iron-bearing district of Michigan. Iron ores; Geology; Geology, Stratigraphic; Geology, Stratigraphic. MAGNETIC! OKSERVATIOXS. 865 the zone of retardation and a lar«iCT over tlie ))oint of no liorizontal deflec- tion, uliicii correspond i-espeotively to the two niaji'netic i-ocks. If the two formations are parallel in strike, l)nt diii away from each other, the cnrves of the horizontal and vertical comjjonents for different anjrles of dij) and different relations of thickness and depth of coverino- are shown in figs. 19 and 20. In fig-. 19 the formations are widely separated, k is relatively small, and the angles of dip are equal and low; the inter- action of the two rocks therefore extends over a narrow zone only, and the curves of the components clearly indicate the presence of two formations and the direction of dip of each. In fig. 20 the anticlinal is so truncated that magnetic material occupies the whole space on the rock surface between the outer boundaries of the two formations. The angles of dip are equal, and are hig-her than in the preceding case, while the depth of cover- ing is relatively much greater. The horizontal component is zero in the axial plane of the anticlinal, and has maximum values at two points, one on each side of the zero. The ver- tical component is a maximum at one point, also in the axial plane. The deflections pro- duced by these conditions could not be distinguished in practice from those produced by a single vertically dipping fomiation. In general, therefore, when two magnetic formations lie within range of each other's influence, the deflections are determined by the relative magnetic strengths of the .two rocks, hj their distance apart, by their strike and dip, and by their depth of burial. It is evident that for certain given relations among these factors the special cases above described will occiu-, and it is found that they really do occur in practice. For other relations it is not possible to make a gen
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectgeology
