PREFACE. 



THE original MS. of the 'Principles of Geology' 

 was delivered to the publisher at the close of the 

 year 1827, when it was proposed that it should 

 appear in the course of the year following, in two 

 volumes octavo. Since that time many causes have 

 concurred to delay the completion of the work, and, 

 in some degree, to modify the original plan. In May, 

 1828, when the preliminary chapters on the History 

 of Geology, and some others which follow them in 

 the first volume, were nearly finished, I became 

 anxious to visit several parts of the continent, in 

 order to acquire more information concerning the 

 tertiary formations. Accordingly, I set out in May, 

 1828, in company with Mr. Murchison, on a tour 

 through France and the north of Italy, where we exa- 

 mined together many districts which are particularly 

 mentioned in the body of this work. We visited 

 Auvergne, Velay, Cantal, and the Vivarais, and 

 afterwards the environs of Aix, in Provence, and 

 then passed by the Maritime Alps to Savona, thence 

 crossing to Piedmont by the Valley of the Bormida. 



At Turin we found Signor Bonelli engaged in the 

 arrangement of a large collection of tertiary shells 



