The xylic and paraxylic acids are separated by the different solubility of their calcium salts, the xylate being the more soluble of the two.

The U.S.A. has a mountain railway which overtops all in Switzerland for altitude, even the 11,333ft of the Jungfrau Railway.

The Obolellida and the basic articulate stock, the billingsellaceans, appear later in the lower Cambrian. The orthide billingsellaceans with their strophic hinge lines, deltidiodont dentition and invariably calcareous shells, comprise two families which, although morphologically similar, have a fundamentally different style of shell secretion, reflected in their various descendants.

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