The shore and dune sand of St. Ives Bay is typically light-coloured owing to the predominance of calcareous matter in the form of shell fragments, etc. But the actual proportion of the platy shell fragments to the heavier and more granular ingredients of the sand varies considerably, especially within the limits of high- and lowwater marks, as is usually the case. Some of the heavier ingredients are dark-coloured, and may be observed to have been streaked out in bands or aggregated in patches at the surface, where they have been concentrated by the action of the waves. Where heavy minerals abound, tidal action can be seen to have effected a persistent concentration about the mean high-water mark, where the heavier ingredients predominate for at least a foot beneath the surface. Such a band can be easily traced for a considerable distance in the vicinity of the Red River.