MATERIALS OF ZONE OF ANAMORPHISM. 669 



As sediments are buried under later sediments, the earlier sediments join 

 the lower zone. Volcanic rocks may join the lower zone either by burying 

 beneath later volcanic rocks or by burying below sediments, or both 

 combined. During their downward movement to the zone of anamorphism 

 they undergo the alterations of the belt of cementation. (3) Any of the 

 products of the belt of weathering may be included within the zone of 

 anamorphism. This may follow as a consequence of the transgression of 

 the sea upon a weathered area and subsequent deep burial under sediments. 

 To illustrate, the rocks of the Piedmont Plateau of the United States and 

 of Brazil are disintegrated to a depth varying from a meter to 90 meters. 

 If the sea transgresses over these regions in the future, as it has in the past, 

 without very active erosion, the weathered zone may be buried beneath 

 later sediments, or volcanics may be poured over the weathered rocks 

 and thus protect them. By deep burying, as a result of volcanism or 

 sedimentation, or the two combined, the entire weathered zone may thus 

 join the lower zone. Finally, it is to be remembered that the weathered 

 rocks which join the lower zone .by burying necessarily pass through the 

 belt of cementation, or have undergone the modifications of that belt at 

 least to some extent, before joining- the zone of anamorphism. 



From what has gone before it is clear that there are considerable 

 variations in the conditions of the zone of anamorphism. The pressure and 

 the temperature vary greatly, depending upon depth, deformation, and 

 igneous intrusions; the quantity of injection varies greatly, the igneous 

 material being here very abundant or preponderant and there altogether 

 absent; the quantity of water, while absolutely small, has a wide ratio of 

 range, being many times more abundant under some conditions than under 

 others. Since this agent, although present in small quantity, is a chief 

 agent of transformation, this variation in the quantity of water is very 

 important. 



Therefore the conditions are exceedingly varied in the zone of 

 anamorphism. Excluding the effects of intrusives, the changes of con- 

 ditions generally take place rather gradually, and changing from one set 

 of conditions to another a considerable vertical depth or a greater lateral 

 distance is commonly required. In this respect the conditions contrast with 

 those of the zone of katamorphism. The contrast is especially marked with 

 the belt of weathering, where the variations in conditions are great and 



