134 Notices of Memoirs — Prof. Helm on Formation of Mountains. 



the part of active eruptive rocks, and have elevated the Alps in 

 thrusting off the sedimentary masses to the right and left. Messrs. 

 Pavre, Suess, etc., on the contrary, regard the central masses as 

 formed within folds. Prof. Heim is of the same opinion ; he shows 

 that all the eruptive rocks of the Alps are much older than the eleva- 

 tion of the chain, which proves that they have merely played a 

 passive part, like the sedimentary rocks themselves, during the eleva- 

 tion. Certain central masses, like that of the Simplon, form large 

 and well-preserved anticlinals. All intermediate conditions are found 

 between this regular form and the fan- structure, which is nothing 

 but an excessive folding. There is no definite separation between 

 the crystalline schists of the central mass and the sedimentary rocks 

 associated with them in the interior of the mass. While the crys- 

 talline schists have ordinarily a high dip, we see them in some 

 places but slightly inclined, and absolutely parallel to the limestones. 

 The unconformities which exist between the two groups of rocks 

 are often not original ; they are produced neither by cooling effects 

 nor by a former elevation, but simply by a difference of movement 

 during the uplift of the Alps. According to Prof. Heim the clearest 

 proof of the inactivity of the crystalline rocks is given by the 

 repeated demonstration — amply detailed in the volume — that the 

 central mass itself has undergone an enormous lateral compression, 

 which by crumpling has reduced this zone of the crust to half its 

 original width. The central masses are then zones of folding of the 

 crust, of a " mechanical facies," only a little different from what is 

 frequently seen in calcareous formations. The difference is perfectly 

 explained by that of the weight which acted on one and the other 

 group of rocks during the lateral displacement. 



The last part of the work is headed " On the structure and 

 formation of mountain chains." The author groups here the results 

 of preceding researches. After an historical account of different 

 views successively put forth on the elevation of mountains, Prof. 

 Heim describes in a general manner different phenomena of 

 dislocation in their interior. The lateral displacement, which he 

 recognizes as sole cause of the formation of chains, can be measured 

 on horizontal sections in stretching out the folded beds. A contrac- 

 tion only of i^o of the earth's circumference would have sufficed to 

 fold the crust in a way to form all the mountains found on the 

 meridian crossing the Alps. 



The remaining chapters contain researches on the distribution of 

 lateral displacement on the surface of the globe, on the relation of 

 different sorts of mountains between themselves and continents, as 

 well as on the proximate causes of their formation. The author, 

 in conclusion, attributes foldings of the crust to the diminution of the 

 diameter of the globe, resulting from contraction by cooling of the 

 internal mass. Prof. Heim estimates at 50,000 metres the diminution 

 of the earth's radius, and thinks that the result would be the same 

 under either hypothesis of the fluidity or solidity of the internal 

 nucleus. 



The analysis above given of this important work is in large part 



