Is the Chalk a Chemical Deposit?

Abstract

The composition of chalk has been shown to consist dominantly of three types of material, in the order of their importance, (1) amorphous, or extremely fine-grained material, (2) spheres, and (3) organic remains.The first, the writer believes, represents chemically precipitated calcite and aragonite, the second a chemically formed oolite, and the last the normal organic constituents.Recent studies have shown that the surface waters of the ocean in favourable localities are saturated with CaCO₃ and that variations in amount of CO₂ mean either solution or precipitation. It is believed that the physical conditions of the Cretaceous sea favoured precipitation. Bacteria may have been a contributing factor.It is hoped that the above suggestion of the possible chemical origin of a part of the chalk (the larger part) will cause those who have the opportunity of study to apply it further, for until the great amount of extremely fine material is accounted for the origin of chalk is not settled. The writer regards the chemical origin with favour because it seeks to explain the origin of chalk in the light of present knowledge of the precipitation of calcium carbonate from sea water.