a. Geol. [f. L. Laurenti-us Laurence + -AN.] A designation of certain sedimentary strata found in Canada near the river St. Lawrence. Also quasi-sb. in collective sense.
1863. A. C. Ramsay, Phys. Geog., v. (1878), 55. The Laurentian rocks are the oldest formations at present known in the world.
1872. W. S. Symonds, Rec. Rocks, ii. 21. The Laurentian, or Basement, sedimentary deposits are divided into two series.
1875. J. W. Dawson, Dawn of Life, vii. 176. The Lower Laurentian of Canada … is found to contain thick and widely distributed beds of limestone.
1876. Page, Adv. Text-bk. Geol., x. 187. The Laurentian strata, till the year 1862, were regarded as metamorphic.
