Edgar Owen noted that in AAPGs Memoir 6, The Trek of the Oil Finders, the first structure contour map ever published was part of a report by Benjamin S. Lyman in 1870, evaluating the oil potential of some lands in the Punjab of India.
But what were the geological experiences Lyman had to enable him to come up with the innovative idea of using contours to depict the geometric shape of specific rock units in the subsurface i.e. structure contours? And why did his first publication involve such a remote geographic area?
Heres the story.
Lyman graduated from college in 1856 and, except for the period 1859-62 when studying geology in France and Germany, worked as an assistant to J. Peter Lesley, a well-known geologist with work experiences dating back to 1838 and the first Pennsylvania Geological Survey.
During that survey the relationship between surface topography and the character of the underlying rock units became clearly recognized, and Lesley began using such topographic relationship in his geologic evaluations. He first used hachures and shading to indicate the steepness of topography, but in 1853-54 he began using contours.
Lyman, through his geological work on Lesleys consulting projects related to coal, iron ores and petroleum in the United States and in southeastern Canada, had to be thoroughly familiar with the usage of contours in topographic mapping and the relationship of topography to the character of the underlying rock units.
Lyman recalled in an 1871 AIME article that in 1865-66, while working on a mining property in Virginia, he had the idea that as contour lines give the best means of showing on paper the shape of the surface of the ground, so they give likewise the best means of showing on paper the shape of the surface of a bed of rock.
Lyman recalled showing a photograph of such a map at an AAAS meeting in 1867, and that he had discussed the innovative usage of rock surface or underground contours with Lesley in 1868.
Lymans mapping procedures were straight forward: determine elevations on the key bed, estimate underground elevations from the measured thickness of overlying units, determine dips and strikes and contour the area with the spacing of contours honoring dip magnitudes and the direction of contours reflecting the strike of the formations.
He noted that with such a finished contour map a structural profile could be drawn in any direction across the map, and that a compIete, true scale geologic profile could be prepared by adding the known stratigraphy to that profile.
In 1869 Lyman probably with Lesleys endorsement was hired by the British government to make a technical evaluation of the oil potential of some lands with oil seeps in the Punjab of India. He spent the following year on that overseas assignment, which resulted in publication by the Indian Public Works Department of a set of 11 structure-contour maps in his Report on the Punjab Oil Lands, Lahore, 1870.
Lyman returned to the United States in mid-1871, but his stay was brief; he was hired in late 1872 by the Japanese government, and until mid-1881 worked on a variety of geological assignments in Japan.
In the United States, the second Pennsylvania Geological Survey (J. Peter Lesley, state geologist) started using structure contour maps with its first reports in 1874. Other state surveys began doing the same. But the first published by the USGS was in its 1886-87 annual report a structure contour map of the Cincinnati Arch, prepared jointly with the Ohio Geological Survey.
A few years later (1893), the first structure contour map prepared by a USGS geologist was published in Bulletin 111 in M.R. Campbells report on the Big Stone Gap Coal Field in Kentucky.
Refinements to Lymans procedures were introduced in 1902 by W.T. Griswold in USGS Bulletin 198. He recognized that when preparing maps on a shallow and on a deeper key bed that when the beds werent parallel a convergence map of the interval between the two key beds could be added to the contours of the shallower bed to make a more accurate structural contour map of the deeper bed.
The convergence map concept was subsequently refined with the terms isochore or vertical interval and isopach or stratigraphic interval being utilized for specific mapping purposes.
Thats how the usage of structure contours to show the geometric shape of both surface and subsurface rock units evolved over time following their innovative first usage by Lyman in 1870. And thats the reason the mapping concept of structure contours was available and ready to be applied by petroleum geologists, as the industry developed following the important oil discoveries at Kern River and Spindletop.