556 THE JOURNAL OF GEOLOGY. 



age so often associated with folded structure. Slaty cleavage, as 

 has been demonstrated by experiment, as well as by field observa- 

 tion, is produced by a mashing together of the whole rocky mass 

 in a direction at right angles to the cleavage plane and a corre- 

 sponding extension in the direction of the dip of these planes. 

 Now since the cleavage dip is usually nearly or quite vertical, 

 this means a mashing together horizontally and a proportionate 

 extension vertically. The amount of mashing together horizon- 

 tall}' and extension vertically has been in many cases somewhat 

 accurately estimated. In this case also, as in folding, we have 

 evidence of a mashing of two or even three into one and a 

 corresponding extension vertically of one into two or even three. 

 This amount of extension affecting thick strata is sufficient to 

 account for the highest mountains in the world without resorting 

 to any hypothetical force pushing upward from beneath. 



There seems therefore to be no reasonable doubt that moun- 

 tains are formed wholly by lateral crushing- with proportionate up- 

 szvelling. This is a very important point gained. Let us hold it 

 fast. This brings me naturally to the next point. 



Infere?ices from § and 6, Granitic Axis and Asymmetric Form. — 

 A granitic or metamorphic axis is a very general, though not a 

 universal, characteristic of mountains. The old idea (still held 

 by some) was that fused matter was pushed up through and 

 appeared above, the parted strata along the crest as the granite 

 axis, lifting the strata, as it were, on its shoulders to form the 

 slopes. But it must be observed that the axis is often only 

 metamorphic, not granitic, and moreover that some mountains 

 are composed wholly of folded strata alone. If, therefore, we 

 regard granite as often only the last term of metamorphism, we 

 may more properly speak of the axis of mountains as metamor- 

 phic. If so, then it is not necessary to suppose any vertical 

 uprising of fused matter by volcanic forces at all. On the con- 

 trary, we would explain the axis thus : 



It is evident that accumulating sediments must cause corre- 

 sponding rise of the interior heat of earth toward the surface so 

 as to invade the lower parts of the sediments and their included 



