Definition of "calcareous"

The traveller from the coast, who, after plodding northward for a score of miles over calcareous downs and corn-lands, suddenly reaches the verge of one of these escarpments[.]

1891, Thomas Hardy, Tess of the d'Urbervilles, volume 1, London: James R. Osgood, McIlvaine and Co., page 15

Cellariiform, the orifices nearly confined to the convex frontal and lateral surfaces; the basal surface with a strong median calcareous keel, almost concealed by a flat membranous epitheca, which covers the whole zoarium […]

1957, Sidney Frederic Harmer, The Polyzoa of the Siboga Expedition, page 1106