[ix-A] The generally received determination of the age of this rock is probably correct; but as there are no overlying coal-measures and no well-known Devonian fossils in the whitish stone of Elgin, and as I have not personally explored the geology of that district, I cannot speak as confidently as in regard to the age of the Montreal Chelonian. [xii-A] H. D. Rogers, Proceedings of Amer. Assoc. of Science, Albany, 1851. [xii-B] See Memoir by the Author, Quart. Journ. Geol. Soc., vol. vii. p. 240. [xiii-A] Wuertembergisch. Naturwissen. Jahreshefte, 3 Jahr. Stuttgart, 1847. [xiii-B] Nov. Act. Acad. Caesar. Leopold. Nat. Cur. 1850, p. 902. For figures, see ibid. plate xxi. figs. 14, 15, 16, 17. [xiv-A] See Manual, p. 268. [xv-A] Manual, p. 289. [xv-B] Ibid. p. 268. [xvi-A] For Terminology, see Note, p. 223. [xvi-B] Quart. Journ. vol. vii. Memoirs, p. 111. [xvii-A] Principles, 1st ed. chaps. v. and ix. [xvii-B] Ibid. p. 153. [xxi-A] Preface to 5th ed. of Studies of University of Cambridge. [xxii-A] Principles, 4th ed. 1835, vol. i. p. 231, and vol. i. chap. 9. subsequent ed. [xxii-B] In my Anniversary Address, for 1851, to the Geological Society, the reader will find a full discussion of the facts and arguments which bear on the theory of progressive development.--Quart. Journ. Geol. Soc., vol. vii. CONTENTS. CHAPTER I. ON THE DIFFERENT CLASSES OF ROCKS. Geology defined--Successive formation of the earth's crust--Classification of rocks according to their origin and age--Aqueous rocks--Their stratification and imbedded fossils--Volcanic rocks, with and without cones and craters--Plutonic rocks, and their relation to the volcanic--Metamorphic rocks and their probable origin--The term primitive, why erroneously applied to the crystalline formations--Leading division of the work Page 1 CHAPTER II. AQUEOUS ROCKS--THEIR COMPOSITION AND FORMS OF STRATIFICATION. Mineral composition of strata--Arenaceous rocks--Argillaceous--Calcareous--Gypsum--Forms of stratification--Original horizontality--Thinning out--Diagonal arrangement--Ripple mark 10 CHAPTER III. ARRANGEMENT OF FOSSILS IN STRATA--FRESHWATER AND MARINE. Successive deposition indicated by fossils--Limestones formed of corals and shells--Proofs of gradual increase of strata derived from fossils--Serpula attached to spatangus--Wood bored by Teredina--Tripoli and semi-opal formed of infusoria--Chalk derived principally from organic bodies--Distinction of freshwater from marine formations--Genera of freshwater and land shells--Rules for recognizing marine testacea--Gyrogonite and chara--Freshwater fishes--Alternation of marine and freshwater deposits--Lym-Fiord 21 CHAPTER IV. CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.