The soil samples were chemically analyzed by a variety of
techniques over a period of time from the mid-1960's to the late
1970's. Details of the methods are given in the references
listed in USGS Open-File Report 81-197 and USGS Professional
Paper 1270.
In summary, the methods used were:
1) Emission spectrography (Myers and others, 1961; Neiman, 1976) for Al, Ba, Be, B, Ca, Ce, Cr, Co, Cu, Ga, Fe, La, Pb, Mg, Mn, Mo, Nd, Ni, Nb, P, K, Sc, Na, Sr, Ti, V, Yb, Y, Zn, and Zr;
2) EDTA titration for Ca;
3) colorimetric methods for P and Zn (Ward and others, 1963);
4) flame photometry for K (Ward and others, 1963);
5) flame atomic absorption (Huffman and Dinnin, 1976) for Hg, Li, Mg, Na, Rb, and Zn;
6) flameless atomic absorption for Hg (Vaughn, 1967);
7) X-ray fluorescence spectrometry (Wahlberg, 1976) for Ca, Ge, Fe, K, Se, Ag, S, and Ti;
8) Combustion (Huffman and Dinnin, 1976) for total carbon; and neutron activation (Millard, 1975, 1976) for U and Th.
The accuracy varies with the analytical methodology and with the
concentration of the element being analyzed. A small portion of
the database contains qualified data. The types of qualifiers in
this data set are:
"N", meaning that the element was not detected at concentrations above the detection limit-this is shown in the data set as, for example, 5.000N meaning that the element was not detected at a concentration of 5 concentration units (ppm or %), the detection limit of the technique.
"L", meaning that the element was detected by the technique, but at a level below the detection limit-this is shown in the data set as, for example, 1.000L meaning that the element was detected by the instrument, but at a level that could not be quantified at or above the detection limit, 1 concentration unit.
"B", meaning that there is no data for that particular element in a given sample-this is shown in the data set as .0000B.
"G", meaning that the element was measured at a concentration greater than the upper determination limit for the technique-this is shown in the data set as, for example, 10.0000G, meaning that the element was measured at a concentration greater than 10 concentration units.
