The Glacial Theory of Prof . Agassiz. 



359 



Mount Jura rises at some points to the height of 5,000 feet* above 

 the sea, and 3,500 above the great valley of Switzerland on its south 

 side. The Alps run parallel to Jura at the distance of fifty miles, and 

 their higher summits have an elevation varying from 11,000 to 15,000 

 feet above the sea ; but the northern skirts of the chain are a great deal 

 lower, and their distance from Jura scarcely exceeds thirty miles. The 

 following diagram will convey an idea of their relative position : 



M V B P, The chain of j,. 



the Alps extending north- 

 east and southwest. 



11, 2 2, 3, The chain of 

 Jura, running parallel to 

 the Alps. 



S S, The great valley of 

 Switzerland separating the 

 two chains. 



G, The lake of Geneva ; 

 N, the lake of Neuchatel. 



The Alps consist of 

 primary rocks, granite, 

 gneiss, &c., in the centre, 

 flanked by secondary. Ju- 

 ra consists of different for- 

 mations of limestone, all belonging to the oolitic series. 



The two chains, in distance, bearing, and position, may be compared 

 to the Ochil and Lammermuir hills. If we suppose the Ochils to be 

 twice, and the Lammermuirs six times as high as they are, and the 

 valley between them, constituting the basin of the Forth, to be three 

 or four times as deep as it is, we shall have a pretty good idea of the 

 physical features of the district under consideration. 



Now the fact which has so long exercised the ingenuity of geologists 

 is this. Hundreds of huge fragments of primary rocks, distinctly re- 

 cognizable as portions of the Alps, are found perched on the southern 

 declivities, or resting in the interior valleys of Jura, forty or fifty miles 

 from their native locality ; and geologists have been perplexed to dis- 

 cover by what agency these erratic blocks have been transported across 

 the great Swiss valley, and placed in the singular situations where we 

 find them. The magnitude, external appearance, and distribution of 

 these masses, present circumstances worthy of notice. 



* The measures are always in French feet, which may be converted into Eng- 

 lish by adding one fifteenth. 



