Finally, the oolitic grains thus produced were cemented together by a further precipitation of crystalline carbonate of lime from the waters of the ocean.
[Illustration: Fig.

14 .-- Slice of arenaceous and oolitic limestone from the Carboniferous series of Shap, Westmoreland; magnified.
The section also exhibit _Foraminifera_ and other minute fossils.
(Original.)] _Phosphate of Lime_ is another lime-salt, which is of interest to the palaeontologist.

It does not occur largely in the stratified series, but it is found in considerable beds [4] in the Laurentian formation, and less abundantly in some later rock-groups, whilst it occurs abundantly in the form of nodules in parts of the Cretaceous (Upper Greensand) and Tertiary deposits.

Phosphate of lime forms the larger proportion of the earthy matters of the bones of Vertebrate animals, and also occurs in less amount in the skeletons of certain of the Invertebrates (_e.g._, _Crustacea_).

It is, indeed, perhaps more distinctively than carbonate of lime, an organic compound; and though the formation of many known deposits of phosphate of lime cannot be positively shown to be connected with the previous operation of living beings, there is room for doubt whether this salt is not in reality always primarily a product of vital action.