Vlll PREFACE TO THE FIFTH EDITION. 



by what paleoutological chai'acters, are discussed in this chapter, pp. 420, 

 447, and 453. 



The relation of the Caradoc Sandstone to the Upper and Lower Silu- 

 rian, as inferred fi'om recent investigations (p. 437), the vast thickness of 

 the Llandeilo or Lower Silurian in Wales (p. 442), the Obolus or Ungu- 

 lite grit of St. Petersburg and its fossils (p. 443), the Silurian strata of 

 the United States and their British equivalents (p. 444), and those of 

 Canada, the discoveries of M. Barrande respecting the metamorphosis of 

 Silurian and Cambrian trilobites (pp. 441, 450), are among the subjects 

 enlarged upon more fully than in former editions, or now treated of for 

 the first time. 



The Cambrian beds below the Llandeilo, and their fossils, are hkewise 

 described as they exist in Wales, L"eland, Bohemia, Sweden, the United 

 States, and Canada, and some of their pecuhar organic remains are fig- 

 ured, p. 447 to p. 453. 



Lastly, at the conclusion of the chapter, some remarks are offered re- 

 specting the absence of the remains of fish and other vertebrata from the 

 deposits below the Upper Silurian, p. 453, in elucidation of which topic 

 a Table has been drawn up of the dates of the successive discovery of dif- 

 ferent classes of Fossil Vertebrata in rocks of higher and higher anti- 

 quity, showing the gradual progress made in the course of the last 

 century and a half in tracing back each class to more and more ancient 

 rocks. The bearing of the positive and negative facts thus set forth on 

 the doctrine of progressive development is then discussed, and the 

 grounds of the supposed scarcity both of vertebrate and inrertebrate air- 

 breathers in the most ancient formation considered, p. 456. 



Chap. XXVIIL — With the assistance of an able mineralogisc, M. 

 Delesse, I have revised and enlarged the glossary of the more abundant 

 volcanic rocks, p. 472, and the table of analyses of simple minerals, 

 p. 475. 



Chap. XXIX. — In consequence of a geological excursion to Madeira 

 and the Canary Islands, which I made in the winter of 1853-4, I have 

 been enabled to make larger additions of original matter to this chapter 

 than to any other in the work. The account of Teneriffe and Madeira, 

 pp. 510, 518, is wholly new. Formerly I gave an abstract of Von Buch's 

 description of the island of Palma, one of the Canaries, but I have now 

 treated of it more fully from my own observations, regarding Palma as a 

 good type of that class of volcanic mountains which have been called by 

 Von Buch " craters of elevation," pp. 494-508. Many illustrations, 

 chiefly from the pencil of my companion and fellow-laborer, Mr. Hartuug, 

 have been introduced. In reference to the above-mentioned subjects, 

 citations are made from Dana on the Sandwich Islands, p. 489, and from 

 Junghuhn's Java, p. 492. 



Chap. XXXV.— XXXVIL— The theory of the origin of the meta- 

 morphic rocks and certain views recently put forward by some geolo- 

 gists respecting cleavage and foHation have made it desirable to recast 



