100 W. P. JENNY 
The southern part of the axis of the Cincinnati arch seems to 
be indicated by a positive magnetic trend. 
Another regional positive trend about parallel with the Cincinnati 
arch may be perceived in the northern central part of Kentucky, 
starting between West Point and Brandenburg and extending south- 
ward to beween Morgantown and Brownsville. 
A third regional positive trend, about parallel with the Pine Moun- 
tain thrust fault, possibly extends from Pine Knot to Hyden. 
The interpretation of the magnetic vectors in Kentucky encoun- 
ters increased difficulties, because the magnetic susceptibility of some 
of the outcropping beds appears to be so great that large magnetic 
“highs” and ‘ows’? may be expected as a result of stratigraphic 
changes only, without any structural significance. Without adequate 
support from geologic data, it is therefore not possible to say whether 
regional trends are mainly due to structural or stratigraphic features 
and the same holds true for the large number of local anomalies indi- 
cated by the vectors. 
The shallowness of the magnetically active horizons should, how- 
ever, prove to be of advantage for the interpretation of local anoma- 
lies, if they are sufficiently detailed by magnetometer surveys. 
SOUTHERN MICHIGAN 
Southern Michigan is a large structural basin, the deepest area of 
which lies between Mount Pleasant, Saginaw, and Lansing. The beds 
dip from all sides at a rate of 25-50 feet per mile toward this central 
area.5 
A sheet of unconsolidated. glacial drift with an average thickness 
of 200 feet covers the whole of Michigan. Below this sheet the Penn- 
sylvanian crops out in the central part of the basin and the Mississip- 
pian, Devonian, and Silurian surround this core in belts of varying 
widths. 
Among the few minor structures known in Michigan® are: the 
Saginaw anticline east and north of Saginaw; the Howell-Owosso 
anticline, extending northwest from Ann Arbor toward Howell, 
Owosso, and St. Johns; the Muskegon anticline north and east of 
Muskegon; and the Mount Pleasant anticline east of Mount Pleasant. 
Different theories have been advanced to explain the origin of 
these folds. They may be connected with the Cincinnati and LaSalle 
5G. W. Pirtle, “Michigan Structural Basin and Its Relationship to Surrounding 
Areas,” Bull. Amer. Assoc. Petrol. Geol., Vol. 16, No. 2 (February, 1932), pp. 145-52. 
° R. B. Newcombe, “Oil and Gas Development in Michigan,”’ Michigan Geol. Sur- 
vey Pub. 37, Pt. 3, Geol. Series 31 (1928). “Geology of Muskegon Oil Field, Muskegon, 
Michigan,” Bull. Amer. Assoc. Petrol. Geol., Vol. 16, No. 2 (February , 1932), pp. 153-68. 
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