II. W. Fairbanks — Contact Metamorphism. 



37 



canic nature of the most of the fragments. The metamor- 

 phosed layer weathers out more strongly, as the photograph 

 shows, than either the dike or the unaltered tufa, forming a 

 prominent and sharply defined band extending up the side of 

 the canon. 



, : ;.;. . ■ .A 



Contact metamorphism in the El Paso range, California. The soft tufa lies on 

 the right of the picture, the slaty contact zone in the middle, the diabase dike on 

 the left. 



In addition to the pronounced manner in which the rock has 

 been baked there is another striking feature. The hardened 

 layer is not massive, but on the contrary, breaks up into thin 

 and regular slate-like slabs parallel to the wall of the dike. 

 The photograph shows the main lines of fissility and the slabs 

 broken off and strewn over the side of the canon. An exami- 

 nation of any one of these slabs shows that it also is thickly 

 penetrated by tine parallel seams which are slightly irregular 

 and discontinuous, but which under the action of the weather 



