8 ON THE~ORIGIX OF MorXTWXs. 



Geikie remarks that, " On the Continent of Europe, the great chains 

 of the Alps and Pyrenees were upheaved in Tertiary times. Home of 

 their rocks, of the same age as the London-clay, have been crystallised 

 and hardened, turned upon end, twisted and broken so as to present 

 very much the character of the Primary rocks of our Highlands. In 

 America the whole backbone of the continent, from the southern end 

 of the Andes up to the Rocky Mountains, got its chief upheaval in 

 Tertiary times." 



Some mountains received their main upheaval at one geological 

 period, while others have been sue upheaved time after time. 



In the Himalayas it is said that there are indications of at least 

 live stages of great upheaval, each of which may have been gradual. 

 There can be no question that all mountains owe their present eleva- 

 tion to upheaval. Fossils have been found at heights of 11,000ft. on 

 the Rocky Mountains, and at over 10,000ft. on the Himalayas. But 

 since the time of their upheaval, partly, perhaps, during their 

 upheaval, they have been worn away or denuded, so that in very few 

 cases do we hud the outlines of the mountain to correspond with the 

 original flexures of the strata. The Jura Mountains form an exception, 

 as their outlines do correspond to the undulations of the rocks. 



Turning now to the causes which have led to such elevations, we 

 may take it for granted that all the strata now forming the mountains 

 were at one time at or below the sea-level. Subterranean move- 

 ments have uplifted them. 



Nearly all mountain ranges have been shown to be composed of 

 strata much bent and folded, to exhibit, in fact, such a crumpling as 

 shows a " diminution of surface area :" and it is considered by Favre 

 that these contortions are due to the cooling of the earth, and the 

 contraction of its radius, composed, as it is, partly of an " interior 

 pasty or fluid nucleus.'' Thus lateral pressure originates, producing 

 contortion, and the consequent elevation of certain tracts, and the 

 depression of others. It has been stated by Prof. Duncan that a con- 

 traction of only l-100th of the earth's circumference would have sufficed 

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

 meridian crossing the Alps.* Hence he considers that the land 

 masses are upward curves on the earth's surface, the ocean floors are 

 downward curves, looking at them in a broad way. Dana calls them 

 " geo-synclinals " and " geo-anticlinals." 



In connection with this part of the subject, it has also been 

 pointed out by Professor Duncan, firstly, that many of the principal 

 mountain chains are at the margins of continents, and that volcanic 

 eruptions take placo where insular conditions are being brought about, 

 or have been brought about in recent geological times, accompanied by 

 parallelism of the chain; secondly, that the proximity of active 



can. Lecture on the Formation of the Main Lund-masses.— Proe. Roval 

 ph. Soc, 187*,Vc.|. XXII. See also O. Fisher, Geol. Magazine, Dec. -Jud, 

 Vol. I, p. 60. 



