Martin, Helen M. 1889-1973. Outline of the geologic history of Hillsdale County, by Helen M. Martin. - [Lansing, Michigan Dept. of Conservation, Geological Survey Division, 1957] - 11 l. maps, diagrs. LCCN: gs 58000148 Subjects--Topical Terms: Geology--Michigan--Hillsdale County. LC Class. No.: QE126.H5 / M3