CHEMICAL ANALYSES AND CALCULATED MODES OF THE OLIVERIAN MAGMA SERIES, MT. WASHINGTON QUADRANGLE, NEW HAMPSHIRE
Complete chemical analyses, including the spectrographic determination of 44 trace elements, have been made of six representative specimens from each of the six map units constituting the Oliverian magma series in the Mt. Washington quadrangle of New Hampshire. Potash is systematically higher than soda. An increase in silica, which ranges from 56 to 75 per cent, is accompanied by the usual variation of the other principal oxides; lime, magnesia, and total iron decrease in the more siliceous rocks, whereas potash and soda increase at first and then decline. Potash is 1.5 to 3 per cent higher than soda throughout the series. With increasing silica content Cr 2 O 3 , NiO, SrO, V 2 O 5 , and BaO decrease, but ZnO increases. Comparisons with other parts of the world, especially northwestern Europe, suggest some systematic differences from New Hampshire, but the data are insufficient to justify any definite conclusions. The calculation of modes from the chemical analyses necessitates a discussion of the methods involved and the possible errors. It is believed that in these rocks the modes can be calculated with relatively small errors. An unexplained excess of alumina in the modes, ranging from 0.0 to 1.0 per cent, may be due to more sericite and clay minerals in the rocks than the content of water suggests.