674 



A TREATISE ON METAMORPHISM. 



(CO) 



(b) 



Fig. 17.— Granulation of feldspar, and gradation between undulatory 

 extinction and granulation, (a) normal anortliosite; (b) granulated 

 anorthosite. After Adams. 



and yet it has almost altogether escaped notice. What stronger mechanical 

 contrast can there be than escape from rupture of all but a very small 

 number of the minerals of a rock and the participation in fracturing of all 

 the mineral particles of a rock? But we shall see that in the zone of 

 anamorphism deformation is largely accomplished by chemical pi-ocesses, 

 whereas in the belt of cementation deformation is mainly accompanied 



by mechanical processes, 

 thus presenting- an even 

 stronger contrast between 

 the two. (See pp.766-768.) 

 The amount of granu- 

 lation varies greatly, de- 

 pending upon the minerals, 

 the size of the particles, and 

 the amount, rate, and other 

 conditions of deformation. 

 Some minerals are much 

 more readily granulated than others. For instance, in many rocks contain- 

 ing quartz and feldspar the former mineral may be granulated while the 

 latter mineral is but little affected. (See fig. 18.) The granulation of a 

 particle may be peripheral or extend throughout 

 the particle. At a stage of deformation, when the 

 smaller particles are granulated throughout, the 

 larger particles may suffer only peripheral granula- 

 tion; in a more advanced stage the larger particles 

 may be granulated throughout; and in some cases 

 of extreme deformation the largest bowlders of con- 

 glomerates are mashed into thin layers not recog- 

 nizable as clastic fragments, each being composed 

 of a multitude of particles. The degree of sub- 

 division by granulation in cases of extreme defor- 

 mation is not usually realized. It should be recalled in this connection 

 that the volumes of particles are as the cubes of their diameters. Very 

 often the diameters of the granulated particles are not more than .1 the 

 diameters of the original fragments; rather frequently the)' are not more 

 than .01, and in some cases they may not be more than .001 of the originals. 

 This means a subdivision of the original particles into 1,000, 1,000,000, 



Fig. 18.— Granulation of quartz in a 

 rock in which the feldspar is but 

 little affected, (a-a) granulated 

 quartz; (5) feldspar. After Adams. 



