262

perhaps the only one, which is wellfounded.

La Metherie a observes, that, during thecrystallization of primitive rocks, theearths were not all dissolved, and couldnot all crystallize; for in these rocks weoften find a quantity of argillaceous mat-ter in an earthy state. Werner speaksof gneiss containing fragments of granite ;and Saussure has shown that brecchias pre-vail in rocks of every age. Mr. Playfair hquotes several instances of arenaceous rocksinter-stratified with rocks decidedly primi-tive ; and greywacke is now very gene-rally admitted into the list of primitiveformations.

It has been proposed to substitute for theterms primitive and secondary rocks, crystal-line % and deposititious; but, unfortunate-ly, rock salt is as crystalline as clay slate,

1 Theorie de la Terre, vol. v. p. 25.

* Illustrations. See also on this subject Dr. Mac-Culloch’s able account of quartz rock in Geolog . Trans,vol. ii. & iv.

e M'Lure, Journal de Physique, vol. xii. p. 145.