It has been supposed, though I do not know who was the first to suggest it, that the total amounts of silica existing in the Chalk with flints and the Chalk without flints respectively are very nearly equal: the idea being that if the quantity of silica disseminated through the flintless Chalk could be accurately estimated it would be found to be nearly or quite as great as the amount existing in the shape of flints in an equal thickness of flinty Chalk.

Proceeding on this assumption it seems also to have been inferred that silica was originally disseminated through the mass of the Upper Chalk, and that this silica has in some mysterious way been concentrated into nodules and layers of flint, leaving the surrounding Chalk in the condition of a nearly pure calcareous material.