20 Anniversary Address of the 



erratic blocks were conveyed to their present sites, or sub- 

 sequently to the glacial period of Northern Europe. 



This assignment to a great number of distinct and separate 

 periods of the work done by the moving and disturbing 

 powers, is by no means the result of the study of the Alps 

 exclusively. In other mountain-ranges it is now ascertained 

 that the upheaving and depressing forces have been propa- 

 gated in succession along the same parallel zones of country ; 

 and M. Elie de Beaumont has frankly confessed that he was 

 in error when he first pronounced the Pyrenees to be a chain 

 due to a single upthrow, " un seul jet," or " une chaine elev^e 

 en une seule fois." He and M. Dufrenoy now go so far as 

 to agree with M. Durocher, that in the Pyrenean chain, in 

 spite of the general unity and simplicity of its structure, six, 

 if not seven systems of dislocation, each chronologically dis- 

 tinct from the other, can be made out.* 



In regard to the Alps, it appears from the observations of 

 Leopold Von Buch, Sir Roderick Murchison, and others, that 

 whatever be the major axis of the crystalline mass in the cen- 

 tre, such also is the prevailing direction of all the sedimentary 

 deposits which lie on either side of the chain. Whether the 

 axis be composed of granite, syenite, gneiss, mica-schist, mar- 

 ble, dolomite, or of any rock formed by eruption or by the 

 metamorphism of pre-existing strata, there is obviously some 

 connection between the position of the central crystalline 

 nucleus and the dominant strike of the flanking deposits. It 

 is as if the intrusion of the igneous matter at certain periods 

 had not only raised the chain, but so injected and distended 

 its central parts, as to force outwards the pliant strata on 

 each side, and to cause them to fold themselves into parallel 

 anticlinal and synclinal flexures. 



The theory first proposed by Von Buch, of the conversion 

 of mountain masses in the Tyrol and other parts of the Alps 

 into dolomite, and of other limestones into gypsum, has been 

 gradually embraced by the majority of the most eminent 

 geologists who have carefully examined the great chain. The 



* Bulletin, 2d Series, vol. iv. p. 1368. 



