AimiVEESAEY ADDEESS OP THE PEESTDES-T. Ivii 



edition of the book. Containing as it does, to begin with, a full ac- 

 count of the minerals whicli form the constituents of rocks, and then 

 giA^ng for the rocks themselves an elaborate description, with copious 

 references to other works, and the synonyms in the German and 

 French languages, it forms a very complete and condensed handbook 

 for the student. The chapters on chemical analysis, on metamor- 

 phism, and on igneous rocks, place within moderate compass and in 

 a fair and unprejudiced hght the results of the works of the numerous 

 authors who, during the last twenty years, have so greatly added to 

 our definite knowledge on these points. The classification and defini- 

 tion of the various species of rock is a notably difficult matter, in 

 which no writer has yet succeeded in giving general satisfaction. 

 Cotta's method will doubtless be objected to by many as starting 

 with an hypothesis of origin which they may be indisposed to admit : 

 the eruptive or igneous rocks, for example, are at once divided into 

 Volcanic and Plutonic, a similar division applying to the basic rocks, 

 or those poor in silica, and to the acidic rocks, or those rich in silica, 

 the latter including, of course, granite and some varieties of gneiss. 

 An arrangement, however, attempted on any other basis, such as com- 

 position or antiquity, must always stumble on difficulties of more or 

 less magnitude until our knowledge is much further advanced. Xot 

 the least useful adjunct of Mr. Lawrence's translation is its very full 

 index of localities referred to in the text. 



Professor Zirkel, of Lemberg, has published during the past year, 

 under the title of ' Lehrbuch der Petrographie,' two volumes contain- 

 ing a vast amount of information on the characters and occiUTcnce of 

 rocks. After a very full general introduction to the subject, be 

 describes in succession all the simple crystalline rocks, or those sub- 

 stances occurring in mass which consist of a single mineral species, 

 — and afterwards the compound crystalline-granular rocks, ranged 

 according to their containing primarily one or other of the various 

 felspars, or belonging to a group which contains neither of them. This 

 first, the original, or the protogenic class of !N'aumann, is followed bj 

 the clastic or fragmentary rocks (deuterogenic), derived from the 

 others by mechanical action. A valuable feature of Zirkel's work 

 is, the abnndant illustration of the peculiarities of each rock-sub- 

 stance by examples taken from the best chemical and geological 

 descriptive writers, with in each case an ample series of references 

 to the literature of that portion of the subject. 



Highly valuable material on kindred matters has been brought 

 together by our able associate. Professor Haughton, of Dublin, in his 

 recent ' ITanual of Geology.' This work, arranged in the form of fif- 

 teen lectures, with sundry appendices, may be considered in the light 

 of a series of condensed essays, which, however useful to students, 

 ofi'er abundant gTOundwork for study and reflection to the practised 

 geologist. The author's contributions to our Quarterly Journal have 

 shoAvn that his elaborate researches on the composition of rock-masses 

 entitle him to speak with weight on the subject ; and I feel that it 

 would be very desirable to endeavour to correlate some of his conclu- 

 sions with those of other inquirers. 



