† 1. ? Brick. Obs.
c. 1340. Cursor M., 5524 (Fairf.). Baþ clay stane and morter.
2. Min. An earthy felspathic rock of igneous origin, and of various dull colors: the harder varieties were known as compact felspar. When breathed on it emits an odor of damp clay.
1777. G. Forster, Voy. round World, I. 149. A kind of brown talcous clay-stone … common to all New Zeeland.
1843. Portlock, Geol., 153. A reddish coloured claystone, amygdaloid, very vesicular.
1850. Dana, Geol., xiii. 584. The claystone has a dark greenish-brown colour.
1851. Mayne Reid, Scalp Hunt. (1863), xix. 113. Smoking out of curiously carved pipes of the red claystone.
1876. Page, Adv. Text-bk. Geol., vii. 134.
3. Comb. Clay-stone porphyry, a clay-stone of more crystalline texture.
1862. Ansted, Channel Isl., II. x. (ed. 2), 271. Shale, occasionally hardening into an exceedingly compact clay-stone, or clay-stone porphyry.
