Montagna — The Metamorphism of Rocks. 361 



of the granite. He remarks that these vegetable remains forbid the 

 idea of heat being the agent in producing the metamorphism of the 

 rocks. And he is confirmed in the opinion expressed in his " Gene- 

 razione della Terra," that granite has been formed solid on the surface 

 of the globe. 



All the serpentines he has observed have yielded fossil plants, 

 as Lepidodendron, Aster ophyllites, Stigmaria, etc. 



Serpentine and ophiolitic rocks of schistose or massive texture 

 show their metamorphic origin in another way ; they have been 

 detected graduating into clay. 



The author has concluded that metamorphism results from mole- 

 cular changes. " The chemical changes that take place in a sedi- 

 mentary rock, and also the formation of a crystalline structure, 

 which we have recognized as the more frequent and remarkable the 

 longer the metamorphic action has continued, are themselves only 

 molecular movements produced by particular combinations and de- 

 compositions due to the nature of the elements." 



The production of these changes he concedes to electricity. 



" There is nothing but electricity which, among the forces known 

 only by their effects, could produce all the phenomena of which we 

 have spoken ; we know no metamorphic phenomenon which it could 

 not explain." 



The origin of lodes may also, he thinks, be explained by electro- 

 dynamic forces. 



Finally he remarks on the constancy and long duration of certain 

 plants being opposed to the metamorphic views of Darwin, and con- 

 cludes by proposing a new classification of the older rocks in 

 reference to the amount of metamorphism they have undergone. 



The three plates illustrate fossil plants from several rocks generally 

 supposed to be eruptive or azoic. 



i2,:B^ri:E]"ws. 



I. — The Production of the Precious Metals : or. Statistical 

 Notices of the Principal Gold and Silver Producing 

 Eegions of the World, Etc. By W. P. Blake, Commis- 

 sioner from the State of California to the Paris Exposition of 

 1867. New York : Putnam and Son. London : Triibner and 

 Co. 1869. 



THIS valuable report, prepared by Mr. Blake at the request of the 

 United States Commission, contains, in as compact a form as 

 such a subject admits of, descriptive and statistical notices of the 

 chief gold and silver producing regions of the world. It differs from 

 the admirable work of Mr. Phillips, published in 1867, in treating 

 less of the methods adopted in the extraction of the precious metals 

 from their ores than of the yield and extent of resource of each 

 country in this particular. The noble metals are considered in suc- 

 cession, and they are discussed, each in turn, in respect to the 

 localities producing them, the statistics of their yield in most cases 



