General Importance of the Data

The importance of the study of the volume, composition, and weight of rocks was the theme of the presidential address of C. C. Moore2 before the Liverpool Geological Society.

The specific weight of a rock, as ordinarily given in textbooks or determined by chemists, is not the weight of the rock, but the weight of the rock powder. In a rock there are always pores, which may be filled with air, gas, oil, or water, and thus it is only in the compact rocks, like granite, where the porosity is very low, that the two expressions, “sp. gr.” and “weight of rock per unit volume,” accompanying chemical analyses, are nearly equivalent, if the latter is given in tons (metric) per cubic meter. I use these units in tables, but in the text, to avoid decimals, I refer to thousands of ounces per cubic foot, assuming . . .

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